Police are, to mix two phrases spanning the Atlantic, the “thin blue line” that “protects and serves”. However, as the legitimate use of force rests with police officers, citizens should be—and are in fact—concerned that force is used proportionately and fairly. Time and again we learn that some police officers use excessive force in a manner wholly unnecessary for a situation (The Guardian 2015), or are unable to de-escalate tense engagements with members of the public (see Piquero et al. 2006; Sherman 1980). Similarly, we know that some citizens’ demeanor promulgates use of force, often through verbal or physical assault of officers (Reisig et al. 2004; Terrill and Mastrofski 2002; but cf. Engel et al. 2000); these instances are likely to result in aggressive arrests and use of more police force. Thus, reducing police use of force is a laudable aim for law enforcement agencies as this can improve public perceptions of police, whilst at the same time making policing more effective (Mazerolle et al. 2013; The White House 2014).
“Force” can be used to achieve a lawful objective, such as making a lawful arrest, subduing a resisting individual, acting in self-defense, or protecting others (College of Policing 2015). However, measuring what “police force” is, at which point it becomes excessive, unnecessary, or disproportionate (Harris 2010)—or even who instigates the use of force beyond what is required—is far from clear (Ariel et al. 2014). There is no tracking system of police force that is completely reliable or even valid—since the amount of “force” necessary in a given situation is subjective, primarily self-reported, and heavily underreported (Hickman et al. 2008). Yet at its core, police use of some force is an essential requirement against certain offenders, under specific circumstances. The issue is not whether or not force needs to be applied, but how it can be minimized.
It is at this juncture that BWCs enter: the basic motivation for police BWCs is, among many other things, to reduce use of force (Miller et al. 2014). The theoretical basis for the use of cameras—that being monitored changes behavior—is deterrence theory (see review in Ariel et al. 2014:4–6). Police BWCs—at least as implemented in our trials—fulfill the causal mechanisms of deterrence to regulate police–citizen encounters. BWCs increase the perceived certainty of apprehension for rule violations. In this sense, the underlying assumption is that officers will use excessive or unnecessary force less frequently than during control conditions. From the citizen/suspect side of things, assaulting the officer, resisting arrest or committing detectable offenses is also bound to lead to further sanctions, which (rational) actors will tend to avoid (see Cornish and Clarke 2014)—a point we return to in the conclusion. When BWCs are actually turned on and appropriately activated, they can efficiently detect rule violations and law breaking by officers and/or citizens—and this process can send a credible deterrence threat (see Jervis et al. 1989:3). In this sense, BWCs are unlike CCTVs (Welsh and Farrington 2009), dashboard cameras, or bystanders’ mobile phone cameras. For a more elaborate discussion on this theoretical mechanism behind BWCs, see Ariel (2016:105–109).
A recent review of the available evidence conducted by Lum et al. (2015) has shown that there are, currently, 12 existing empirical studies of BWCs and about 30 ongoing research projects (see also review by White 2014). While there were attempts to implement BWCs in policing nearly a decade ago (Goodall 2007; Harris 2010), evidence on their effectiveness has only surfaced in the last couple of years (see Lum 2015). Four of the studies employed randomized controlled trials (Ariel et al. 2014; Grossmith et al. 2015; Jennings et al. 2015; Owens et al. 2014), and others have used less robust designs (e.g., Ariel 2016). The most recent published studies employed different units of analysis to measure various consequences of the use of BWCs in police routine operations: in Orlando, Florida, the unit of analysis was the individual officer (Jennings et al. 2015); Ready and Young (2015) compared volunteers versus non-volunteers, while others have used a version of cluster random assignment (Grossmith et al. 2015). Lesser designs, without random allocation of units into treatment and control conditions (e.g., Ariel 2016; Ellis et al. 2014), have produced mixed results about the effectiveness of BWCs, ranging from supportive evidence, to null, and even backfiring effects.
The Rialto experiment (Ariel et al. 2014) was the first randomized controlled trial that looked at the effectiveness of BWCs, and specifically focused on use of force and complaints. Rialto Police Department, a jurisdiction in California with just over 50 frontline officers, compared nearly 1,000 police shifts during which all police–public encounters were equally assigned to either treatment or control conditions. During treatment shifts, Rialto officers were asked to record (audio/video) all their encounters with members of the public and to store evidence on a secured cloud. In the control shifts, the officers were instructed to never carry the devices. Outcomes were then measured, in terms of officially recorded use of force incidents and complaints lodged against Rialto police officers. Following this 12 months experiment, Ariel et al. (2014) reported a relative reduction of roughly 50 % in the total number of incidents of use of force compared to control conditions, and about a 90 % reduction in citizens’ complaints, compared to the 12 months prior to the experiment.
Ready and Young (2015) conducted an experiment with the Mesa, Arizona Police Department. The study analyzed nearly 3,700 field reports completed by 100 sworn patrol officers. Random assignment of the officers into treatment and control groups has resulted in several important findings: first, officers who did not wear body worn cameras were more likely to conduct stop and search, and were also more likely to make an arrest. This means that wearing BWCs may cause officers to be more cautious and risk-averse than officers in control conditions. At the same time, treatment officers were more likely to give citations and initiate encounters. This suggests that BWCs may cause officers to be more proactive with this technology, however without increasing their use of invasive strategies that “may threaten the legitimacy of the organization” (Ready and Young 2015:445).
Finally, Jennings et al. (2015) have also observed the effect of BWCs on policing, but focused particularly on response-to-resistance incidents. In their controlled experiment, they randomly assigned 46 (of 89) officers to wear BWCs, with the remaining 43 officers assigned to a no-BWC condition. The study has shown that BWCs reduced these types of incidents and serious external complaints. The prevalence of response-to-resistance incidents and the prevalence and frequency of “serious” external complaints were significantly less for officers randomly assigned to wear BWCs (p. 480).
These studies suggest that the credible deterrent effect of BWCs may rest on four critical points: that the camera is (i) actually worn by the officer, (ii) turned on, and (iii) used during the police–public encounter. It also requires that (iv) suspects are fully cognizant of the BWC, for instance through officers announcing to the suspect that the interaction is being officially recorded. If the officer applies discretion and does not record an encounter—for whatever reason—then the deterrent effect of the camera will be nil. To use a medical analogy, one must take a pill in order for it to be effective.
It is precisely the issue of discretion where we believe that the effect of BWCs can vary, and the continued debate around police officers’ discretion is at the core of our present analysis. “Police work is complex [,] police use enormous discretion [, and] discretion is at the core of police functioning” (Kelling 1999:6). Discretion underpins policing by consent (Leyland 2012). Yet “discretion” per se is a vague term that broadly reflects the decision-making power afforded to officers with the aim of allowing them to decide whether or not, and to what extent, to follow police procedures (Hirby 2015). Codified rules and regulations often limit the use of discretionary powers—for instance in the area of mandatory arrests for domestic violence (see review in Hirschel et al. 2007), shooting at moving vehicles (e.g., Alexander City Police Department 2008), holding suspects in a chokehold position (e.g., NYPD Patrol Guide 2013), or the use of ‘enhanced interrogations’ on suspects under extreme circumstances. However, in the area of use of “force”, the guidelines are suggestive: the force continuum, which is meant to align the appropriate amount of force to various scenarios in order to de-escalate the situation, can be overridden based on the officers’ subjective perception at the time of the incident (see Watson et al. 2008). It is only with the clear vision of hindsight that a “forceful incident” might be deemed to have resulted from an abuse of decision-making powers. The core of the analysis presented below is to understand what role police discretion plays in the emergent area of police BWCs.