Mass spectrometry-based proteomics for the forensic identification of vomit traces

Proteomics was exploited to assess the nature of possible traces of vomit found on the scene of an alleged sexual assault. In the case in point, a woman reported to the police to be raped five days before by a cousin of hers in his car. The woman declared she had vomited in the car before fainting definitely, due to alcohol or possible drugs covertly slipped in her drinks. The suspect confirmed the sexual intercourse, but he claimed consensual sex while the woman was fully conscious. To establish consent and hence subsistence of the crime, the Magistrate requested toxicological analyses on items sampled from the car and from woman's boots. Negative results obtained from toxicological analyses could not exclude the actual assumption of psychoactive substances by the alleged victim, due to sample aging. On the contrary, proteomic analysis disclosed a pattern of 249 gene products including signature endogenous and food-derived proteins along with a multitude of peptide digests, clearly indicative of vomit, thereby supporting the victim's report in the case under examination. Proteomics also provided detailed information about the nature of meal, which might contribute to frame the crime scene in similar cases. SIGNIFICANCE: The identification of traces of vomit supported the report of the victim's report according to which she vomited before definitely losing consciousness, so providing key contribution to establish consent for the sexual intercourse. This is the first time that proteomics is used to identify traces of vomit for forensic purposes. In spite of the scantiness of the biological specimen available, proteomics was successful to define a panel of characteristic endogenous proteins as well as to identify partly digested food-proteins arising from a complex meal. Proteomics is increasingly used as a forensic technique, well complementing the existing tools. In general, assessing traces of vomit in biological specimens and characterizing the nature of food ingested at the molecular level could afford probative elements to frame a crime scene.