Latent fingerprints were developed after submergence in water from all the eight surfaces used in this study. The quality of prints developed in relation to the two variables studied, i.e. duration of submergence and succession of prints, is depicted in Tables 1, 2, 3, 4, 5, 6, 7, and 8. The developed latent fingerprints, submerged as well as successive, on all the selected substrates are shown in the tables in the Additional file 1.
Overall 400 prints were developed and examined in this study. Half of the total prints (200) were developed using Robin powder blue, of which 174 prints were identifiable with a score of 3–5 and only 26 prints were not properly identifiable with score 2 or 1. However, in case of commercially available silver magnetic dual powder, 25 prints developed on the aluminium foil surface had negligible contrast and hence were discarded. Remaining 175 prints were developed by silver magnetic powder, in which 152 prints were identifiable with a score of 3–5 and only 23 prints were unidentifiable with score 2 and 1 (Fig. 1).
The best quality identifiable prints were obtained on glass (Tables 9 and 10), laminated paper, and floor tile surfaces with 49, 48, and 48 (out of 50) prints respectively with a score of 5, 4, or 3. In addition, floor tile, debit card (red), and painted iron saw surfaces gave 44, 43, and 39 (out of 50) identifiable prints with a score of 5, 4, or 3, respectively, while 21 (out of 50) prints remained unidentified on credit card (golden glitter) surfaces with a score of 2 or 1. In this order, Robin blue powder provided a better quality of prints on credit card (golden glitter) as compared to silver magnetic powder. The reason behind the low quality of print was the conflicting glitter of silver magnetic powder as well as golden glitter of the credit card which rendered poor contrast with the developing powder. On aluminium foil, none of the prints could be developed/visualized with silver magnetic powder due to poor contrast while only one print developed out of the 25 prints, by Robin powder blue, was poor (Table 11).
It is known that the quality of latent fingerprints naturally deteriorates over time (Baniuk 1990; Yuille 2009; Archer et al. 2005; Midkiff 1993), and our results are also similar to this. In this order, only 2 prints (out of 75) were not identified, when they were developed after 0.5 h and 24 h. However, when these prints were developed after 48 and 120 h in water using a similar method, the quality of developed prints significantly deteriorated. After 48 and 120 h in water 11 and 32 (out of 75) prints, respectively, were scored 2 or 1. Our results show that prolonged submergence deteriorates the quality of developed prints (Figs. 2 and 3).
Our results are in accordance with Castello et al., who found that up to a submersion time of 3 days, the development results were similar for the glass and plastic surfaces with 4 or 5 grades on scale which indicates clear well-identified prints. From the fifth day, significant differences in print development were observed (Castelló et al. 2013). Similarly, some other studies (Soltyszewski et al. 2007; Devlin 2011; Stow and McGurry 2006; Madkour et al. 2017; Trapecar 2012a, b; Rohatgi et al. 2015; Trapecar and Pantic 2017) were also in consensus with the result that the clarity of the prints decreases with an increase in submersion period. By extending the duration of submersion in water, the number of developed useable fingerprints were reduced, and more finger marks remained undeveloped.
It is a well-believed principle that ‘everything changes with the passage of time’. There are various changes that occur based on several factors along with the time duration (Cadd et al. 2015). The lengthier the duration, the greater is the degradation (Girod et al. 2012). Additionally, the water-soluble components of the fingerprint residue are more prone to destructive forces such as water, high temperatures, and low humidity (Iten 2012; Barnum and Klasey 1997). If a print is wetted, then the aqueous components of the print are removed, thereby leaving less available components for the powder to adhere to, but the enhancement is still possible and is reported in the current study and in literature (Dhall and Kapoor 2016). On analysing the impact of succession of prints, it was found that the score decreases with subsequent prints. In the first, second, and third prints, a total of 8, 5, and 6 (out of 75) prints respectively were unrecognizable with a score of 1 or 2, while in the fourth and fifth subsequent prints, 11 and 19 (out of 75) were unidentifiable with a score less than 3.
The procedure adapted to fingerprint deposition on the surfaces was uniformly maintained to have consistent quality prints before submersion. After all, the results are dependent on the initial prints too. A systematic process can also result in inconsistent fingerprint deposition. There are certain factors that influence latent fingerprint deposition; some may be controlled while some may not be (Fieldhouse 2011). It is unlikely that the chemical and physical composition of two fingerprints will be identical, thus affecting the credibility of conclusions made. Factors associated with the donor (chemical composition) include smoking, illness, medication, age, gender, race, and diet. The factors associated with fingerprint deposition (physical) include force applied during deposition, duration of surface contact, angle of surface contact, substrate, and residue quantity due to washing.
This study is restricted to simulated stagnant water conditions in a laboratory setup, while the natural water bodies that are encountered during investigations of crimes are diverse from laboratory condition. They are subject to a number of internal and external factors including temperature, wind, aquatic flora and fauna, pH, precipitation, and enclosure.