29 Jul 2020
New forensic technique for identifying semen in sexual assault cases could revolutionise rape investigations
- First demonstration of direct mass spectrometry to chemically profile semen, showing the unique combination of chemicals could be used to confirm the presence of semen faster and more reliably than current techniques
- Analysis of both fresh and aged semen, with this new method, has shown that it is still possible to identify semen weeks after deposition, which is important in criminal investigations where evidence may not be recovered or analysed immediately
- Residues from condoms produced strong chemical profiles, with different brands of condoms producing unique profiles, potentially offering information about the type of condom used by an offender
A pioneering new technique for detecting semen on evidence from the scenes of sexual attacks will make evidence gathering faster and more reliable for police as well as less stressful for victims.
Scientists at Loughborough University have developed a method which uses a small needle surrounded by solvent to collect samples that are then analysed by a mass spectrometer for an instant positive or negative result.
The test can also confirm whether or not a condom was used and could potentially identify the brand.
Lead author of the paper Stephanie Rankin-Turner, a postdoctoral research associate from the department of chemistry, said the technique would speed up the forensic process and lessen the victim’s anxiety of waiting for evidence.
She said: “This technique was developed to provide a faster and more reliable means of analysis, with the ultimate aim of speeding up investigations.
“Evidence backlogs have been a major problem in the past, with samples sitting in evidence lockers waiting to be analysed.
“By allowing investigators to quickly confirm whether or not a substance is semen, the time spent waiting for analysis of potential semen samples can be reduced, ultimately speeding up an investigation.
“Long, drawn-out investigations can obviously be very stressful to victims, so we want to provide technology to make investigations and evidence analysis more efficient.
“Furthermore, as people are becoming increasingly aware of DNA profiling, more offenders are using condoms.
“In the absence of biological evidence such as semen, the possibility of detecting traces of condom use can help support a victim's statement.”
The current techniques used by investigators destroy any samples during the testing.
They are also non-specific, said Stephanie.
Which means they can produce a positive result with other substances, misinforming police and potentially slowing an investigation.
Although the tests were carried out in a lab, Stephanie says test kits could be portable and give instant results.
She said: “Although in the study we used laboratory-confined instrumentation, this technique is readily coupled with portable mass analysers that could be used on site for rapid and direct analysis.
“This evidence could then either be analysed back in the laboratory or, potentially, in situ.”
Future research could also identify chemical changes in the samples, giving investigators a method of estimating the age of the semen, which could further corroborate victims’ statements.
Details of the pilot study, Using mass spectrometry to transform the assessment of sexual assault evidence, have been published in the journal, Forensic Chemistry.