Investigation of condom evidence in cases of sexual assault: Case studies

Abstract

Previous research has established analytical frameworks and discrimination models for the analysis of commercial silicone-based and water-based lubricants, but there has been no report of the application to casework. The analytical framework was first tested on two proficiency trials to validate the methodology on cotton swabs. Then two case samples, where condoms were suspected of having been used, were submitted to the laboratory for analysis. Examination of vaginal swabs for condom evidence was performed, independent of knowledge regarding the presence of seminal fluid or other sources of DNA. Pyrolysis-Gas Chromatography mass spectrometry (py-GC-MS) and Gas Chromatography mass spectrometry (GC-MS) were used to analyze the evidence and compare the chemical profiles obtained to published databases. The protocol was successfully used on two proficiency trials, one in which py-GC-MS chemical profiles were easily differentiated, and the second in which GC-MS was used to identify the source of the chemical profile on the recovered item. Although the application to casework samples was possible, challenges regarding the interpretation of the evidence were highlighted and need to be considered by forensic practitioners.

Keywords

• Py-GC-MS
• Silicone
• Polyethylene glycol
• Condom