Trace evidence is the basis of all forensic work. When a person comes into contact with an object, minute material is exchanged between the two, building the narrative for cops and prosecutors – in theory, at least.
But some criminals have learned to cover their tracks. For instance, a growing proportion of rapists are using condoms to limit the amount of DNA and body fluids. A recent federal study found that a third of approximately 2,000 Los Angeles rape investigations yielded no DNA.
Candice Bridge, a University of Central Florida chemist, is working on developing a new tool which could assess condom lubricants to help forensically connect criminals to an assault where DNA is not available.
So far, some classes of lubricants are detectable at trace levels. But Bridge, in a recent interview with Forensic Magazine, said the most-advanced chemistry tools is providing a window into a whole new avenue of placing a condom, and a criminal, at a sexual-assault scene.
“There hasn’t really been a lot of lubricant research in America,” said Bridge. “People carry around condoms – both men and women. And most of them are lubricated. So, the question becomes – what can be gathered and what capabilities do we have with lubricants?
“In the absence of biological evidence, what else can we do to identify a link between a suspect and the victim?” she added.
The National Institute of Justice has awarded Bridge and her laboratory a $324,000 grant to pursue the investigative leads – which could add condoms, lubricants, and even prophylactic wrappers, to the detectives’ toolbox.
The ultimate goal is that victims, or their underwear, may have traces of distinctive lubricant. That lubricant could be matched on the suspect, on their clothing, or in their condom collection – further narrowing down the field, Bridge said.
“There are thousands and thousands of lubricants out there,” she said. “Most of them are silicone-based. If there’s any way we can narrow down the field, to say, ‘this was used in the commission of the crime’ – and you find a suspect that has personal lubricant or is carrying the condoms… that provides another link.”
The NIJ grant follows a major study published by Bridge and one of her postdoc students recently in the journal Forensic Science International.
The study assessed 33 common personal, water-based lubricants found in condoms. They used a technique called direct analysis in real time-time of flight mass spectroscopy (DART-TOFMS). They found that six difference groupings within the chemical makeup of the samples. Those grouping correlated with additives in condoms such as anesthetics, sensation enhancers, and even flavorings.
What remains is to continue to catalogue the condoms in use out in the world – and to cross-reference their proportion of compounds like glycerol, ethoxydiglycol, phenoxyethanol, propylene glycol, butylene glycol, lidocaine, and benzocaine.
“This will provide a baseline to potentially enable lubricant analysis to be implemented in sexual assault cases,” they conclude in the study.
The NIJ grant is going to enable that work to move forward, Bridge said. Currently the work in her laboratory is focused on silicone-based lubricants – a pending study has identified six or seven different categories among those kinds of marketed products, as well, she said.
“Now we’ve been able to demonstrate there are subclasses available, whether you’re using IR or mass-spec,” she said.
Bridge said the DART-TOFMS tool is accurate and fast – you can get an active ingredient in a compound, plus most of the fillers, in a short 10 seconds or less. Her students place dollar bills on the scanner, and quickly determine how much cocaine is on them from the bills being in general circulation.
“At the end of this, we’ll have a publicly-available database that can be used by the community,” she said.
The work remains to compare the technique to PCMS and IR – both of which Bridge has experience with. (She has also published work on gunshot residue, among other topics).
Bridge, currently an assistant professor in the UCF Department of Chemistry, grew up in New Jersey. She earned her doctorate from UCF at the age of 25, and has previously worked at the U.S. Army’s Defense Forensic Science Center.