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Publication
Reverse body fluid identification workflow: a direct to DNA Approach
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Advisor(s)
Abstract(s)
When forensic DNA laboratories receive evidence from a crime scene their first task is to check for the presence of biological material, namely blood, semen or saliva; the same principle is applied to clothing or swabs related to victims from sexual assault cases. Examination of the exhibits by naked eye or using a forensic light source is done in order to detect the presence of body fluid stains. Many laboratories perform preliminary tests on items where biological material is potentially present before sending a cutting or swab for extraction and subsequent DNA typing.
To identify the presence of body fluids our laboratory has implemented presumptive and/or confirmatory assays to detect semen, blood and saliva and, until the end of 2022, all samples selected for DNA extraction and posterior amplification were also tested to determine the type of biological evidence in question (whenever enough sample was available) in two independent workflows.
For semen identification, all presumptive positive results were then tested in order to visualize sperm cells. However, in sexual assault cases there are many samples with a semen presumptive positive result but with a negative confirmatory test, meaning that this biological fluid cannot be confirmed.
On the other hand, it was detected that in several situations the analysed samples did not present probative DNA results and, consequently, it would not have been necessary to test them for the presence of bodily fluids.
The aim of this study was to propose a more efficient workflow to be applied to all forensic samples
647 samples from sexual assault crimes (male/female victims), occurred between 2020 and 2021, were selected and the results obtained in both previously mentioned workflows were evaluated and compared with a Direct to DNA approach, in which DNA analysis is performed prior to body fluids identification (carried out only on samples with eligible DNA profiles for the criminal case under study).
The results revealed that if a Direct to DNA approach was adopted, only 256 samples (39,6%) would have been tested for the presence of semen (confirmed in 80 samples). Therefore, this workflow (currently implemented in our laboratory) is less laborious and time-consuming, allows standardization of the techniques implemented and, above all, no loss of information relevant to the judicial process was detected
Description
Póster apresentado no 30th Congress of the International Society for Forensic Genetics, 9-13 setembro 2024, Santiago de Compostela, Espanha
Keywords
Sexual assault Body Fluid Identification Semen Detection Direct to DNA Approach