A Systematic Literature Review of Specialist Policing of Rape and Serious Sexual Offences

The policing of rape and serious sexual offences (RASSO) is increasingly under scrutiny, with rising reporting rates, high attrition rates, and ever-decreasing charge and conviction rates. Internationally there appear to be common inadequacies in RASSO investigations. Given these issues, policing specialism may be an effective tool to improve the investigation of RASSO. This article systematically draws together the existing literature from around the world on the use of a specialist approach to tackling RASSO. A systematic literature review was conducted, and 18 papers were included for analysis based on the inclusion/exclusion criteria. From these documents, five key themes were found: investigation procedures and processes; victim care; specialist training, knowledge and skills; officer wellbeing and capacity; and policing outcomes. The review highlighted that the specialist policing of RASSO can improve the investigative process on several levels: improving the efficacy of the individual components of the investigation; better engagement with victims; better officer wellbeing; and overall improved policing outcomes. Further research is required into the specific mechanisms that results in improvements into the investigative process, the set-up of such specialist units, as well as how training in this area can be as effective as possible.


Introduction
While there is no universal, agreed upon definition as to what is encompassed by the term 'specialism' in policing, Westmarland et al., (2012, p. 28) set out a working definition of rape teams as having 'dedicated, trained staff working together in an integrated way to provide the highest quality victim care and investigative standards'. In this way, the concept of specialism can be seen to encompass several different factors, including the advent of specialist units/teams to handle different types of crime, the development of specialist training, and the acquisition of specialist skills and knowledge relevant to the crime in question.
Child abuse, gang crime, and cyber-crime are just some of the types of offences that have dedicated specialist police units in the majority of forces in several countries, including the United Kingdom (UK), Australia, and the United States of America (USA; Harkin et al., 2018;Martin et al., 2017;Valasik et al., 2016;Willits & Nowacki, 2016), with recommendations for specialist police teams for other types of crime and policing such as tourism and art in Europe and the UK (Mawby et al., 2015;Runhovde, 2021). A common justification for specialism in policing is the unique knowledge and skill each crime investigation requires. For example, gang crime entails specialised skills in intelligence gathering, including covert surveillance, and specialised knowledge in gang member affiliations and associations in studying patterns of gang activity (Valasik et al., 2016). In child abuse crimes the police have two roles, that of investigators and child protection. High levels of stress and emotional strain inherent to child protection work is placed on police officers investigating these crimes and, therefore, specialist training in personal resilience and mental preparedness is seen as paramount to undertaking the unique duties in investigating child abuse safely and effectively (Martin et al., Charlotte T. Dalton and Sophie Barrett are Joint first authors who made equal contributions to the paper. 2017). Technical expertise and workload management are skills specific to cyber-crimes. The enormity in size and scope of cyber-crimes, their ever-changing context as well as continual technological advancement regular training and development are seen as essential for the investigation of this type of crime (Harkin et al., 2018;Willits & Nowacki, 2016).
These different types of specialist knowledge required for the investigation of different offence types, as outlined in this previous research, should lead to several types of outcomes: (i) better investigation of offences, leading to better charge (and potentially conviction) rates; (ii) better protection and safeguarding of victims, and (iii) the protection of officer wellbeing (Harkin et al., 2018;Martin et al., 2017;Valasik et al., 2016;Willits & Nowacki, 2016). The importance of specialism in some crimes, and the effect it can have on these outcomes, can be demonstrated in the impact when that specialism is no longer present. A temporary disbandment of a specialised unit for gang crime in Los Angeles in the USA, for instance, led to a decrease in intelligence gathering and reduction in the number of gang arrests. This temporary disbandment continued to impact gang crime investigations even after the specialist unit was reinstated, with a slow return to pre-disbandment levels of intelligence collection and arrests (Valasik et al., 2016).

The Specialist Policing of Rape and Serious Sexual Offending
In the last decade, the policing of rape and serious sexual offences (RASSO) has come under increased scrutiny, with high attrition rates and ever-decreasing charge and conviction rates, despite a rise in reporting of these offences. In the year ending 2019-2020, there were 618,000 female victims of sexual assault recorded in the UK [with 58.7% the proportion of suspects charged for rape/volume of suspects charged 1867] (Her Majesty's Inspectorate of Constabulary and Fire & Rescue Services [HMICFRS], 2021a;CPS, 2021). Reports across constabularies of HMICFRS and the Criminal Justice Joint Inspection (CJJI) found common inadequacies in RASSO investigations, specifically in the timeliness of investigations and evidence collection, delays in the apprehension and changing of suspects and cases reaching court, and poor victim engagement and support including the presence of victim blaming throughout the criminal justice system (CJJI, 2021;HMICFRS, 2021a).
There are several challenges unique to the investigation of RASSO which suggest that taking a specialist approach to this type of crime may assist in the improvement of its policing. RASSO is a serious crime mainly perpetrated against women (HMICFRS, 2021a). The presence of rape myth acceptance, gender stereotyping, and victim blaming, found to exist in the criminal justice system and society at large (Rollero & Tartaglia, 2019;Sleath & Bull, 2012;Stoll et al., 2017) poses a specific challenge to RASSO investigations. Rape myth acceptance and victim blaming has been widely researched and is found to detrimentally impact on the success of RASSO investigations and convictions and the mental health of the victim, lengthening their recovery time and increasing the risk of re-traumatisation (Grubb & Turner, 2012;Maddox et al., 2011;Moor, 2007). Multiple studies highlight the need to address these misconceptions to avoid any harmful impact on RASSO victims and on RASSO investigations and prosecution (Page, 2010;Rich, 2019;Sleath & Bull, 2012) and specialist knowledge and training may be required to adequately target these issues.
The trauma associated with being a victim of RASSO is also an aspect of policing that requires specialist treatment, as the police's perception and understanding of the victim's experience is essential in laying the foundation as to how the victim experiences the investigation process, with officer engagement having the potential to limit any possible effects to the victim's mental health and recovery process, or to re-traumatisation and re-victimisation (Maier, 2008;Moor, 2007). The necessity for an informed and empathetic approach in engaging with the victim is further complicated in the different suspect and victim relationships found in RASSO crimes. In the majority of cases the suspect is known to the victim and cross overs with investigations of domestic abuse can therefore occur, causing complexities in evidence gathering and clarity of role and responsibility between police departments which inexperienced officers of RASSO cases may not be equipped to manage, and which the high levels of victim attrition during the course of a RASSO investigation-particularly that which occurs in the early stages of the investigation after first contact with the police-would support (Elkin, 2018).
The investigation of RASSO involves working with potentially traumatised victims who may require additional safeguarding. As in child abuse cases, dealing with these issues may place additional emotional strain and stress on officers who may require specialist knowledge, training, and support to be able to effectively continue to work in the area. Similarly, the additional safeguarding concerns seen in child abuse offences may also relate to RASSO. Although recent reports have found an improvement in the response to sexual offences in the risk assessments, safeguarding measures, and victim support put in place (HMICFRS, 2021a), the high attrition rate (Home Office, 2020) and general low satisfaction levels seen in victims (HMICFRS, 2021b) suggests more needs to be done in this area to better support and protect victims.

Drawing on Organisational Theory
There are several organisational change theories which are widely used to understand, evaluate, and support changes within policing and its organisational structure, as found in research on gang crime and community policing (Weisel & Painer, 1997;Katz et al., 2002;Maguire et al., 2000;Mastrofski & Ritti, 2000). Although the purpose of this literature review is not to apply organisational theory to the current practice and structure of RASSO investigations, drawing upon organisational theory and linking to policing structure and behaviour can be useful to identify necessary changes needed for an organisation to be successful. Specifically, contingency theory is a way to understand the organisational structural changes that are being proposed in this paper in the creation of specialised RASSO teams. In contrast to institutional and resource dependent theories which see other institutions and external resources as an integral part of change in organisations, the underpinnings of contingency theory are those where behaviours, practices, and structures within the organisation adjust to meet their goals (Crank & Langworthy, 1992;Pfeffer & Salancik, 1978). Contingency theory proposes that organisations are rational entities which modify and adapt to achieve their objectives (Crank & Langworthy, 1992;Maguire, 2001). In their dynamism and goal centric approach, contingency theorists would argue that organisations will seek out change to address performance issues so that they remain efficient and effective (Mastrofski & Ritti, 2000). Considering the rise in reporting of rape and serious sexual assaults, the high number of 'no further action' (or NFA) outcomes, along with poor conviction rates, contingency theory would argue that as an organisation, the creation of a specialised RASSO unit is a logical response to the changes in the current environment and the need to adapt to this change to remain effective. Indeed, studies have found that police forces that have significant problems in specific areas of crime such as gang crime, have responded to this by setting up specialised crime units, demonstrating the application of contingency theory into practice (Needle & Stapleton, 1983;Weisel & Painter, 1997). Furthermore, contingency theory proposes that organisations who do not adjust accordingly do not prosper and even do not survive (Lawrence & Lorsch, 1967). Contingency theory, therefore, not only supports organisational adaptation in response to environmental contingencies, with contingencies regarding RASSO being seen in the changes in reporting and conviction rates to meet its goals, but also sees it as a necessity of its survival.

The Current Review
Given the issues with the investigation of RASSO, the number of potential areas in which specialism may be an effective tool to improve the policing of RASSO, and the dearth of any systematic attempt to review the evidence base of dedicated RASSO units (van Staden & Lawrence, 2010) it is an appropriate time to undertake a review of the literature about the specialist policing of RASSO. This article aimed to systematically draw together the existing literature from around the world on the use of a specialist approach to tackling RASSO, including how it could contribute to tackling the challenges associated with these types of investigations.

Search Strategy
The search strategy involved an iterative process to define broad keywords, and to search for both academic documents and grey literature on the subject. For the academic document searches: four well-established academic databases were selected for the search process: Applied Social Sciences Index and Abstracts [ASSIA]; Criminal Justice Database; Proquest-Psychology; and Web of Science. These databases were selected for their accessibility, quality and range of information provided, and their scope of relevant disciplines covered including criminology, psychology, and sociology (Brophy & Bawden, 2005). For the grey literature searches: Google Scholar was used for a targeted search to gather any material pertaining to policing specialism, such as policing or governmental policy documents.
Due to the expectation of limited research available, keywords were kept broad. Variations of the keywords were used to avoid excluding relevant papers based on wording, for instance 'specialist', 'specialism', and 'specialised'. Other keywords included: 'police', 'law enforcement', 'criminal justice', 'crime', 'unit', and 'team'. No RASSO specific keywords were used to gather all articles on police specialism, regardless of policing area or crime type, where RASSO articles were later separated. The words 'team' and 'criminal justice' were rejected where they did not yield any relevant articles and were perhaps too broad. The word 'crime', similarly broad, was only kept in conjunction with 'unit' (i.e. 'crime unit'), and 'law enforcement' was only used on the database Proquest Psychology, where search results returned were insufficient on the other databases. This was initially included, where it was considered that terms might differ from 'police' internationally. On all databases, words were searched in the title and abstract only, to eliminate any papers did not have a targeted focus on police specialism. Table 1 shows the final keywords and search strings used.

Article Screening
Studies were downloaded from the databases, duplicates removed, and then the final 1277 documents for review were uploaded to literature review software Rayyan, where a further 25 duplicates were excluded. Rayyan was used to organise and code data, allowing for ease of collaboration, including measurement of interrater reliability (Ouzzani et al., 2016). To test for interrater reliability, the two lead researchers blind coded 165 papers, or 13.34% of the total number of documents for review (using the criteria outlined below). Four conflicts were found, giving an overall agreement rate of 95.78%. In these incidences, one researcher had included two papers that were not policing focused; this error was corrected. The other two disagreements were based on the ambiguity over the inclusion of specialist training focused papers (coded as 'not specialism focused'); it was decided that these would be included thenceforward. Once the interrater reliability exercise was complete, the remaining documents were divided in half for the lead researchers to review individually.
For the initial screening, the abstract and title of each article was assessed and included if it met all of the following inclusion criteria: -(For the academic literature) a peer reviewed document; -Written on or after 1990; -Policing focused; -Specialism focused; -RASSO focused; -Full text available.
Papers were labelled as 'include', 'exclude', or 'maybe'. Any articles marked as 'maybe' were discussed by both reviewers to decide whether to include or exclude the paper for final screening. For the 18 papers progressed to final screening, the whole article was read to check it adhered to the above inclusion criteria, all were included. The search process and number of documents identified at each stage is outlined in Fig. 1.

Results
A total of 12 academic articles and six official reports were included in the review (see Table 1 for a summary of these papers) ( Table 2).
From these documents, five key themes and seven subthemes were found and shown in Fig. 2.

Investigation Procedures and Processes
Several studies focused on the impact that specialism, particularly the existence of specialist RASSO teams, had on different outcomes, with RASSO specialist teams outperforming non-specialist teams in several investigative areas, including evidence gathering, crime recording, and interviewing, timeliness, and multi-agency working (Powell & Wright, 2012;Rumney et al., 2019;Rumney et al., 2021;van Staden & Lawrence, 2010).

Evidence Gathering, Crime recording, and Interviewing
Research suggests that police performance in RASSO investigations improves when undertaken by a specialist team, through the better co-ordination of investigations and more accurate crime recording van Staden & Lawrence, 2010;Westmarland et al., 2012). Specifically, a greater consistency of concise and ethical recording was found in cases carried out by specialist RASSO teams (Westmarland et al., 2012), along with a higher quality of investigation plans in most case reviews examined in the CJJI report (2021). In addition to succinct case notes, Westmarland et al.'s (2012) report listed greater opportunity to carry out targeted research and intelligence gathering under specialist teams alongside the presence of streamlined forensic strategy. The handling of evidence in general was found to be widely impacted upon by whether the RASSO investigation was undertaken by a specialist team or not. Studies found that under specialist RASSO teams there was a reduction in the risk of evidence not being collected (van Staden & Lawrence, 2010), and that other investigative undertakings, such  (2012) found that specialist officers were more informed about what was needed from the interview as well as having a better understanding of the victim's experience. Indeed, it is these skills and knowledge which guide appropriate and tactical questioning, and which have been found to impact the openness of the victim and their ability to access information of the crime, as well as their continued cooperation in the investigation (Powell & Cauchi, 2013;Tidmarsh et al., 2021a).

Timeliness
The timeliness of RASSO investigations was mentioned in many studies and reports on police specialism, an area which has been highly criticised in inspection reports (CJJI, 2021). There was general agreement that timeliness of RASSO investigations improved when specialist teams exist, with victims noting a timelier response received by specialist RASSO officers in comparison with non-specialist officers (Darwinkel et al., 2013). Powell and Wright's (2012) study on professionals' perspectives on rape investigations concurred, finding shorter investigation and charge times in specialist teams. The importance of timeliness in RASSO investigations was particularly linked to the collection and handling of evidence, with van Staden and Lawrence's report (2010) finding reduced delays in time-sensitive investigative actions in cases run by specialist teams. This finding is supported by the 2021 CJJI report in their observation of fewer delays in specialist team run investigations due to more appropriate choice of evidence, with an average time of 49 days for specialist and 108 days for non-specialist teams.

Multi-agency Working
Multi-agency working with the Crown Prosecution Service (CPS) is an important aspect of the RASSO investigation process, with enhanced collaboration found to improve communication and encourage sharing of information, allowing for a smoother investigative process as well as continuing to provide sufficient and consistent support for victims (Powell & Wright, 2012;van Staden & Lawrence, 2010). Specialist teams have been found to have a better working relationship with the CPS (van Staden & Lawrence, 2010), including having a greater frequency of direct communication between the CPS and specialist officers, in comparison to some specialist officers who had never had direct communication with a prosecutor (Westmarland et al., 2012). Improved relationships and increased contact between police and the CPS were also found in cases carried out by specialist teams, aiding the progression of cases and impacting on the timeliness of the investigation (van Staden & Lawrence, 2010). The importance of support for RASSO investigations is demonstrated by Rumney et al.'s (2019) report which found referrals to support services reduced the rate of victim withdrawal. This finding concurs with CJJI report (2021) which notes the absence of a victim centred approach and lack of sufficient support leads to victims withdrawing their consent. Indeed, some papers highlighted the impact of multidisciplinary sites. Primarily sourced from Australian studies, it was found that the co-location of support services relevant to RASSO, such as counselling, medical care, and forensics were widely welcomed by victims. It was found that having the relevant services all on one site allowed victims to have anonymity and enabled immediate access to services when they needed them such as counselling (Hansen et al., 2015;Powell & Cauchi, 2013;Powell & Wright, 2012). In addition, it was found that as a neutrally independent facility, multidisciplinary centres influenced a victim's continued participation in the investigation (Powell & Cauchi, 2013;Westmarland et al., 2012).

Victim Care and Engagement
All the reviewed studies and reports on police specialism addressed, to some degree, the importance of victim care in investigating RASSO cases. In general terms, victims that engaged with specialist rather than non-specialist RASSO teams felt as though they were treated as valued complainants and felt respected during the investigation process (Powell & Cauchi, 2013;Westmarland et al., 2012). Powell and Cauchi (2013), for instance, found that 92.9% of the victims being assisted by a specialist team were happy with the investigative process, compared with 55.6% of those seen by a non-specialist team. In addition, 72% of victims working with a specialist team would recommend reporting assaults to others. This theme explores two facets of victim care which could influence overall victim satisfaction during the investigative process, including communication with victims, as well as victims' access to support services.

Communication with the Victim
A lack of communication with RASSO victims was a prominent theme in the literature on specialism with its presence in half of the papers and with both police and victims highlighting the importance of regular communication about the progress of the case (Jamel et al., 2008). Stark statistics on absence of communication was presented in the CJJI report (2021) which found a quarter of NFA cases did not record whether the victim was told of the closing of the case, although this could also be due to poor record keeping. Despite this, the CJJI report did find better communication in police forces which had specialist teams (2021). This aligned with other studies' findings where communication with the victim was found to be more 'streamlined', with specialist teams having designated officers with clear roles which allowed for consistent and focused victim engagement (Powell & Wright, 2012;Rumney et al., 2021;van Staden & Lawrence, 2010). Specifically, improved communication with victims found in specialist RASSO teams was linked to the recruitment of specialist officers dedicated to the communication with victims van Staden & Lawrence, 2010). These designated officers were deployed quicker after reporting and had more time for post-incident liaison, allowing the officer time to build a rapport from the outset van Staden & Lawrence, 2010). They were also found to have better quality of communication because the designated specialised role meant there were no competing pressures from being reassigned to non-RASSO cases (CJJI, 2021;van Staden & Lawrence, 2010). This greater consistency of police personnel was linked to an increase in the victim's satisfaction and wellbeing during the investigation and was found to reduce the chance of miscommunication and limit the detrimental effects felt by victims in relaying details of the offence, often found when multiple officers are involved with victim liaison during the investigation van Staden & Lawrence, 2010). In addition, being kept apprised of the progress of the investigation was found to affect victims' acceptance of the status of the case even if advice differed to their expectations (Powell & Cauchi, 2013;Powell & Wright, 2012).

Support Services
Sufficient victim support and referrals to Independent Sexual Violence Advisors (ISVAs) were key components of victim care shared across a minority of papers, with all finding higher levels of support and referrals in specialist RASSO teams compared to non-specialist teams. Specialist RASSO teams outperformed non-specialist teams in the rate of referral to ISVAs, which was in turn linked to a greater allocation of dedicated victim engagement officers in specialist teams van Staden & Lawrence, 2010). In van Staden and Lawrence's (2010) study, whilst the role of the ISVA itself was not found to have changed because of the specialist unit, the benefits of police-ISVA co-location as part of these specialist teams increased police understanding of the ISVA role, highlighting the importance of their presence during the investigation (CJJI, 2021;Powell & Wright, 2012;van Staden & Lawrence, 2010). Furthermore, victims were more likely to engage with the police in the investigation if an ISVA was involved which was facilitated by the specialist units (HMICFRS, 2021a).

Specialist Training, Knowledge, and Skills
Seven of the twelve studies found on policing specialism in RASSO focused on specialist training, knowledge, and skills, with the 2021 CJJI report highlighting that expertise and specialist knowledge is created through exposure to RASSO cases, knowledge which is lacking in non-specialist officers (2021). This training or experience is a mechanism through which aspects of the investigative process and victim engagement and care can be improved, facilitating a better RASSO investigation. It was widely agreed amongst specialist RASSO officers that specialist skills and knowledge were required to investigate these crimes effectively due to the complexities in the crime that are unique to RASSO, such as the victim and suspect relationship and evidence collection, understanding and undertaking appropriate engagement with the victim, interviewing both suspect and victim, and the experience and confidence to undertake tasks in difficult investigations (Tidmarsh et al., 2021a). Indeed, Westmarland et al. (2012) observed similar findings with officers noting the importance of understanding a victim's reaction to rape and the reasons for late reporting, insight non-specialist officers were felt not to have. Specialist police also noted the importance of empathy, good communication, and open mindedness as qualities required in RASSO investigations (Tidmarsh et al., 2021b). To acquire these skills and knowledge, officers need to gain experience, either through training or on the job experience. Learning skills without initial training takes time, however, with the CJJI report noting that 'the right skills, training and understanding need to be deployed from the outset' (2021, p.76), otherwise non-specialist officers who have limited experience and understanding of RASSO cases can lead to longer delays in the investigation, something which was not found in specialist teams (2021,2021).
Several studies focused on the importance of specialist training in RASSO cases and the positive effect this has on officers' perception, understanding, and approach to RASSO investigations. One example of how training can lead to the types of improvements noted above is the effectiveness of specialist interview training on an officer's use of best practice questions and relationship evidence, with research demonstrating a positive effect on non-sexual grooming details and the long-term use of relationship details, as well as an increased use of open questions and a decreased use of closed questions (Tidmarsh et al., 2021a). Rich (2019) looked at the importance of what questions are asked in RASSO interviews as well as how the victim is interviewed, highlighting the need for specialist training for officers to conduct interviews in a trauma-informed manner to avoid potential revictimisation and addressing the presence of rape myth acceptance (RMA) in the police.
Training also impacts on investigative efficacy, specifically in the manner that victims are treated, and an area of particular importance is specialist training used to address RMA and stereotypes for officers working on RASSO cases (Rich, 2019). A study on predictors of RMA found that specialist training significantly predicted RMA, with officers who were sexual offences investigative techniques (SOIT) trained having a lower RMA than those who were not (Murphy & Hine, 2019). However, when training was tested against individual variables, SOIT officers held the perpetrator responsible in an acquaintance rape but not in a partner rape, where they saw the perpetrator as less responsible compared with officers with no training (Hine & Murphy, 2017). The dominance of attitudinal variables over training concurs with Lonsway et al.'s (2001) study which found that specialised training was effective in improving behavioural performance but not cognitive or attitudinal outcomes. These findings demonstrate the importance of the training applied to be sufficient and appropriate to the task to ensure its effectiveness. Furthermore, frequent follow-up training is also necessary to stop skill erosion, often found after some time has passed since training (Tidmarsh et al., 2021a).

Officer Wellbeing and Capacity
As well as the effect of specialism on the investigative process and the level of service provided to victims, a specialist approach to RASSO policing has the potential to affect the officers working in these roles, both through their sense of team cohesion and the resources dedicated to the investigation of these types of offences.

Team Cohesion
A common finding across multiple studies was a sense of team cohesion in specialist units which created a support network amongst officers and showed their commitment to RASSO investigations (Powell & Wright, 2012;Rumney et al., 2021). This was found to encourage collaboration and increase communication between the ranks of specialist RASSO staff and across police departments (van Staden & Lawrence, 2010). The clarity of the role and responsibility amongst specialist RASSO officers compared with nonspecialist officers Westmarland et al, 2012) was also found to be important, with a clear separation of the investigative role from the victim liaison role seen as positively impacting on the timeliness of the investigation and on communication with the victim and general victim care Westmarland et al, 2012). While not specifically discussed in the articles reviewed, other research demonstrates that this type of cohesion, collaboration, and communication amongst officers increases their wellbeing, in return promoting resilience in a high-stress work environment. Powell and Wright (2012) remarked that the success of specialist RASSO teams was dependent on suitable officers being recruited. This statement was supported by other research which found that officers who had specifically applied for a position in a specialist RASSO were more engaged with the work contributing to a sense of common purpose Westmarland et al., 2012), with poor quality investigations and victim care being linked to officers reluctant to investigate RASSO cases . One of the few downsides to specialism noted in the reviewed articles, however, was the reluctance of official agencies to resource specialist units, with concerns raised over both the cost and resources required to staff such units (Westmarland et al, 2012(Westmarland et al, , 2015. A lack of resources, too large a geographical area to cover, not enough RASSO specific offences, and a desire to have detectives competent in all crimes were reasons not to have a specialist RASSO team (Westmarland et al., 2012). In the same studies, however, there were also findings of cost effectiveness of RASSO units and agreement of resourcefulness found in specialist teams, demonstrating the need for further research in the challenges of resourcing in specialist teams.

Policing Outcomes
Carrying out RASSO investigations in specialist teams has been linked to higher charge, prosecution, and conviction rates (Powell & Wright, 2012;Rumney et al., 2021;Westmarland et al., 2012). These increases could be attributed to the improvements outlined above to the investigative processes and victim care through increased training and knowledge, as well as better resourcing and officer wellbeing. There is some evidence in the literature that directly linked some of these factors. For instance, the ACPO report (2015) produced a three level model of the elements required for improved policing outcomes, where RASSO investigations in general CID are the basic level, specialist teams with a victim care focus (e.g. Cheshire DRU) improve victim support but cannot show improved conviction rates, and specialised units with the above and a proactive perpetrator focused approach meant they were able to conclude with confidence that specialist units lead to an attributable increased in convictions. A suspect focused approach and improved victim care are key aspects found in fully developed RASSO teams . There is contention over whether a specialist approach makes a tangible difference to conviction rates. Some papers reviewed commented that they could not accurately evidence that specialisation improved convictions, despite other improved outcomes (van Staden & Lawrence, 2010;Westmarland et al., 2012). These papers were regarding short-term pilots of specialist teams, or teams that were recently established, for instance, in van Staden and Lawrence's (2010) study, the pilot project was operational for six months. These papers were qualitative and based on the perceptions of practitioners, a valid a useful approach, yet, the ACPO (2015) was able to quantify outcomes. Where improved convictions rates were only established in three studies, further research is recommended.
Given the low charge and conviction rates seen in RASSO investigations as a whole, these outcomes are important, but they are not the only policing outcomes that could be used as measurements of specialist team 'success'. Decreased victim attrition could be another way of measuring success in this instance, as a marker of victims' confidence in the officers dealing with the investigation and the criminal justice process as a whole (Powell & Cauchi, 2013). The impact of specialist RASSO teams on victim withdrawal in relation non-specialist teams varied across studies. Hansen et al. (2015) explored attrition rates in the early stages of rape investigations between victims in contact with a specialised multidisciplinary treatment unit compared to those who were not. They found no significant differences in attribution patterns or legal reasons regarding case closure between the two groups. Rumney et al. (2021), however, found that specialist teams retained a higher number of complex vulnerable victims compared to non-specialist teams, demonstrating the effects of the differing approach to the investigation and engagement with victims and between the specialist and non-specialist teams.

Discussion
The objective of this review was to determine the scope of existing literature regarding police specialism in RASSO investigations. Literature is evidently limited and primarily based on pilot studies of specialist units, yet it begins to give a picture of the potential successes of such an approach. Research encompasses the impact of dedicated specialist teams and knowledge on investigative performance, victim experiences, officer wellbeing, and justice outcomes. In general, literature noted benefits in all the above areas, as well as improved multi-agency working, with an enhanced victim experience at the centre of this. Overall, most of the evidence supports the use of specialism.

What Should our Measures of Success be?
When talking about specialism, as noted in the introduction, the term actually encompasses several different concepts that this review has tried to draw out and more explicitly define. Measures of success, and the mechanisms through which they are achieved, need to be clearly defined so that any positive change can be replicated and trialled elsewhere. The literature reviewed here demonstrates that success can be measured in several different ways. First, we can look at overall policing outcomes in terms of charge rates. This is a key aspect of specialism as the current charge rates, in the UK and abroad, are extremely low. While many of the studies were based on self-reported improvements, thus making it difficult to objectively measure success in terms of charge rates, there is some evidence that specialism in policing does help to improve RASSO charge rates.
Charge rates, however, are not the only measure of success, as even in cases of police NFA, specialist units were evidenced to reach faster decisions because of fewer investigative delays, and to communicate this to the victim via more appropriate methods, suggesting that improving the individual investigative components is helpful beyond measurement at charge level. Considering the disturbance that delays in the criminal justice process can cause to victims' recovery, mental health, work, relationships, and general disruptions to life (Burnham & Brooks-Hay, 2020), specialist units appear better equipped to provide a more satisfactory victim experience, potentially reducing the effects of secondary victimisation that RASSO victims are distinctly vulnerable to (Moor, 2007), even when a charge decision is not reached. Further, information gathering, and record keeping were both shown to improve under specialist units, which can impact positively on other investigations, due to better intelligence and evidence. For instance, a more streamlined response means time sensitive evidence may be less likely to be missed, resulting in cases where a victim declines to prosecute but subsequently chooses to re-open the case may be more likely to proceed (Powell & Cauchi, 2013;van Staden & Lawrence, 2010;, or links to other investigations may be made. It is important to note that there is only some evidence that in specialist teams it was less likely that evidence was lost when victims decided to re-engage later (CJJI, 2021), meaning that further research is required to understand the impact of specialism has on the investigative process.
Charges are not necessarily the only measures of success from the victim's point of view. Victims' perceptions of justice can be dynamic and vary from person to person (McGlynn & Westmarland, 2018); for instance, in some cases, the victim might perceive making a formal statement as successful engagement with the criminal justice system should this experience be positive, regardless of the justice outcome (Robinson, 2009). In the papers reviewed, procedural justice-or the fairness of the process-was evident in specialist teams (Powell & Cauchi, 2013;Westmarland et al., 2012), in line with findings in comparable research regarding specialist domestic violence investigations, where improvements to victim care and overall experience with the police and criminal justice system (as well as to the investigative process) are evidenced within specialist teams (Friday et al., 2006;Klein & Crowe, 2008). Success here can be measured, both in terms of retaining a higher number of complex vulnerable victims through the criminal justice process (Rumney et al., 2019, as well as levels of victim satisfaction with the process (Powell & Cauchi, 2013).
Finally, officer wellbeing, whilst again may be related to successful charge outcomes, is also a measure of success. This is an area of research that requires further exploration, however, as it was the most underrepresented measure of success in this review and did not include measures of professional wellbeing such as effective supervision, or opportunities for career development and progression. Even though officers working in specialist RASSO units demonstrated increased communication and were encouraged to collaborate, working in a ringfenced unit exclusively could also mean greater exposure to traumatic, emotionally complex material, and high pressure or high stress situations. If appropriate support is not available, officers in specialist units may be more susceptible to stress, burnout, anxiety, vicarious trauma, secondary traumatic stress, or other detriments to wellbeing seen in other areas of policing, such as those policing indecent child images (Perez et al., 2010) or involved in child protection (Anderson, 2000). Other professionals working with RASSO show evidence of similar detriments, for instance, frontline staff at a Sexual Assault Referral Centre reported emotional numbing in relation to the volume, unpredictability, and specific nature of the work (Massey et al., 2019).

What Should Specialist Units Look Like?
While most of the reviewed literature here spoke of the advent of specialist units and their impact on the measures of success as outlined above, often the specific reasons why these specialist units improved performance were not explicitly explored (specialist knowledge and training being an exception; further details below). Some benefits of specialist units were highlighted, such as co-location which seemed to improve multi-agency working, but this is an area of the literature which requires further research to establish exactly why these units prove to be successful. Understanding the set up and individual roles of each unit member is important, for example, and it may be possible to draw on comparisons from other offence types here, such as murder, where officers work on one case as a team and take on different roles in each case. Given the complexity of the offending, the interaction with a victim who may be traumatised, and the often repeat and varied nature of offending, there is certainly an argument for RASSO offences to be investigated by a team of officers, although it is important to caveat this with ensuring that all officers, regardless of the role they hold in each case, hold the specialist knowledge intrinsic to effectively investigating RASSO.
When discussing specialist units, the seeming lone downside of policing specialism-that of resourcing-is relevant here. Ensuring that a specialist team is properly implemented, and that they have access to the information, resources, and training required to effectively conduct a RASSO investigation, all requires resourcing which is necessary if law enforcement want to see meaningful change in this area. Selective specialism may be an answer to some of the resourcing concerns, such as having specialist interviewers within a team of specialist RASSO officers, although again this is caveated heavily with the fact that the core facets of specialism essential to the role need to be understood and mastered by all working in the units, even if they are taking on different roles at different times.

What Should Specialist Knowledge and Learning Look Like?
The review found several ways in which officers could attain the skills and knowledge required to operate in specialist RASSO teams; through the application of qualities brought to the role by the officer, such as empathy and open mindedness (Tidmarsh et al., 2021b), through exposure to RASSO cases (CCJI, 2021), and through specialist learning delivered to officers working in the units. Exploration of all these factors is required to ensure that the right officers are undertaking the role of specialist RASSO investigator and given the right tools to do so. First, there is the question of eligibility. None of the articles found any evidence of screening processes or the application of a particular job criteria to qualify officers for the role of RASSO specialist, something which may require consideration if there are inherent qualities required. These factors may be able to be acquired by experience or training, and if so, this needs to be considered when developing the experience and training officers have access to. The difference between experience and training needs to be considered here in terms of understanding and separating out the information that can be learned 'on the job'. It is likely there is information that cannot be learned through experience and instead requires dedicated training; furthermore, there is information that will be critical for officers to know from the outset of their role rather than developing this knowledge over time. For instance, the stereotypical and erroneous views held about rape that are prevalent in society are equally likely to be present in officers' views, and dedicated training should be used to educate officers as to the realities of rape and the responses of traumatised victims so that prejudicial views are not carried into investigations.
If specialist officers require additional training, this means considering how this training is delivered and the efficacy of this delivery. There are instances in the reviewed literature where training was found to be effective only at the level of behavioural performance, rather than promoting and instilling cognitive and attitudinal change (Lonsway et al., 2001), and evidence in other areas of research strongly suggests that the way training is delivered has a significant impact on the efficacy of said training. The lack of current effective training may go some way to explaining that, even where policing outcomes show improvement in areas where specialist units exist, charge rates remain low overall.

Implications for Practice, Future Research, and Limitations
Most of the research is based on professionals and victims' perceptions of specialist units and, whilst this is a valid way of determining success, other measures of success would strengthen the argument for specialism, such as reviewing case file information to more objectively assess investigative efficacy. Further, much of the research assessed changes over a relatively short period of time and follow up research is required to understand more about the long-term impact of specialist units on success. In terms of the review itself, it deliberately sourced international material to see whether comparisons could be drawn about the benefits and challenges of different specialist police practices around the world; however, most of the reviewed documents were UKbased, with the exception of some studies from Australia, and one from the US, and Denmark. It is likely that UK policy documents were more easily found given that the authors are based in the UK, and further work could be done to source more international policy documents pertaining to specialism.
While this review has discussed the opportunities and challenges associated with the specialist policing of RASSO, there may be cross-cutting areas of specialist knowledge that could apply to several areas of policing, suggested by some of the similarities noted in the traumatic nature of investigating both child abuse and RASSO. There are also likely to be similarities between the issues related to violence against women and girls that span both RASSO and domestic abuse offences, and work could be conducted to see where in an area where resources are often stretched, how specialism or specialist training could be combined or shared across different specialist units. Similarly, as noted above, there may be elements of the role that could be conducted by a few officers within the specialist unit, such as dedicated RASSO interviewers, although much of the skills and knowledge required to undertake this role effectively, such as the knowledge of how to interact appropriately with traumatised victims, are skills that all RASSO officers should have.
While this review has assessed the effect of specialism on RASSO policing on the investigative process and on policing outcomes, it is important to note that these factors alone cannot be considered a success as they do not reflect the entire law enforcement process. Regardless of police performance, difficulties still exist in ensuring the process is fair, such as the presence of rape myths and stereotypes that persist beyond policing and through other areas of the criminal justice system. Research has demonstrated, for instance, that these attitudes are both present and hard to combat in jurors (Leverick, 2020), with guidance to jurors shown to have limited impact on adherence to specific rape myths (Ellison, 2019), for instance, information regarding the false perception of physical resistance as the standard reaction to sexual assault had little impact on adherence to this view (Ellison & Munro, 2013). As with the training in policing on this issue, the way this training is conducted needs careful consideration to ensure its effectiveness and that this efficacy endures.

Conclusion
This review has highlighted that the specialist policing of RASSO can improve the investigative process on several levels, improving the efficacy of the individual components of the investigation such as interviewing and evidence collection, better engagement with victims, better officer wellbeing, and overall improved policing outcomes. This was facilitated most notably by the increase in specialist knowledge and training officers brought or had access to. Further research is required into the specific mechanisms that result in improvements into the investigative process, such as the set-up of such specialist units, as well as how training in this area can be as effective as possible. Specialism should also be considered in terms of its core functions and whether certain areas of specialism are fundamental to RASSO only or whether they are also functions of better policing in other types of offences.
Funding The funded was provided by Home Office.

Declarations
Conflict of interest The authors declare that there is no conflict of interest.
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