Identifying the culprit from LCN DNA obtained from saliva and sweat traces linked to two different robberies and use of a database

Abstract

This work refers to the identification of a criminal who committed, during a period of 6 months, two robberies in two different towns in Northern Italy. In the first robbery, we analyzed traces on a pillowcase used to carry the stolen goods. As the pillowcase showed no visible traces, we made a specific search for latent traces by means of a Crimescope CS-16 tunable forensic light source used in a special darkroom at a wavelength ranging from 415 to 490 nm: it revealed some interesting luminescent areas possibly due to biological traces (saliva). Subsequently, the latent stains were analysed with the alpha-amylase test, which gave positive results. The evidence available for the second robbery consisted in a pair of glasses left by the criminal in a bank. The glasses showed no visible traces, however, the surface in contact with the nose and ears were sampled using FTA-Paper to collect any residual sweat. The use of the database for the management of DNA profiles allowed us to link the two crimes that had occurred in two different places and at different times. In fact, the same complete male profile for 15 STRs was obtained both from the traces of saliva identified on the pillowcase used to carry the stolen goods (first robbery) and from the glasses frame surface which had been in contact with the nose (second robbery). Moreover, these results enabled the extraction of low copy number (LCN) DNA from uncommon evidence left at the crime scene, increasing the possibilities to identify the culprits.