Genetic profiling of enhanced fingerprints deposited on military firearms

Most of the forensic investigations conducted within the Brazilian Army are crimes against property. In this scenario, fingerprints analysis represents an important investigative tool. However, given the fragility of fingerprints, even after development with suitable techniques, failure in identifying its authorship may occur. In these cases, studying the DNA transferred to the surfaces during the fingerprints deposition may represent a timely approach. In this study, we aim to investigate the feasibility of profiling fingerprints deposited on armaments utilized by the Brazilian Armed Forces after enhancement with White Powder (Sirchie®). Therefore, five IMBEL M964 (FAL) rifles and five IMBEL 9 M973 gun pistols were decontaminated with sodium hypochlorite 2.5% and alcohol 70%. The weapons were manipulated by three volunteers (Brazilian Army personnel) as it would be done in a routine set. Five areas of interest in each type of armament were chosen for swabbing before and after fingerprints enhancement. After the use of dactyloscopic powder, only areas where prints were obtained were swabbed. Samples were collected with sterile swab humid with distilled water, DNA was isolated with Lysis Solution methodology and concentration of the extract was accomplished with Amicon® 100 column. Quantitative analysis was carried out with Quantifiler™ Human kit and StepOnePlusTM Real-Time PCR System, both by Applied Biosystems. Samples were amplified with PowerPlex® CS7 kit (Promega Corporation) and profiled in the ABI Prism® 3500 Genetic Analyzer platform. Quantification results showed a decline in the average DNA recovery from samples after fingerprint enhancement: 54pg/µL to 32pg/µL (rifles) and 148pg/µL to 21pg/µL (pistol). However, the presence of fingerprinting enhancement powder did not appear to hamper the acquisition of genetic profiles as much as the quantity of the DNA template available. Sixty percent of all fingerprints revealed from the armaments returned a full profile and in correlation with real-time PCR results these samples had above 200pg of extracted DNA. Two aspects were observed in this study: the inevitability of obtaining mixed profiles, as 53% of total samples collected showed contamination probably due failure in decontamination process and the inherent ability of each person in donating cells through skin desquamation during contact with surfaces, which is a critical not controllable component in DNA touch analyzes. Regarding all rifles’ samples (with and without enhancement), from one of the volunteers only 22% of full profiles were returned and in contrast, 100% of full profiles were generated for another volunteer. Also, allele recovery rate for rifles (82%) were greater than the same rate for pistols (56%) which was attributed to some of the rifles features: it is heavier resulting in more pressure applied to the surface by the fingers, larger area for contact and it is usually held by the military during the service for longer periods of time. The composition of the armaments is also a subject for further investigation as they are different mixtures of metal alloy and high strength polymer which may affect the success in obtaining a full genetic profile. Based on the obtained data, an oriented collection is suggested in the following areas: trigger, grip panel and slide (pistols) and stock, hand grip and handguard (rifles). Total alleles recovery rate: 71% and 82 % respectively, 100% compatible with the reference profile. The continuity of such study with the expansion of sample space will allow the production of statistically robust data and the effective development of guidelines for the improvement of military conduct in criminal investigations.

SOBRE O TEXTO:
Texto de autoria de Ludmila Alem ², e co-autores Valentin, E.S.B. ¹; Santos, O.C.L ¹; Silva, D.A. ² Nogueira, T.L.S. ¹,²
¹ Instituto de Biologia do Exército, Rio de Janeiro, Brasil;
² Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brasil;

Foi submetido e aprovado para apresentação oral na Conferência Internacional Interforensics 2017, sendo originado a partir de trabalho desenvolvido no Laboratório de Ciência e Tecnologia Forense da UERJ.