To find rapists, Candice Bridge examines what condoms leave behind

On an April day in 2001, Candice Bridge ran out of a storefront in the middle of the night, chasing a medical examiner’s van down the streets of Washington, DC.

“I need to talk to you,” she said, surprising the man behind the wheel. It was 1:00 a.m.

“I could have shot you,” he scolded.

This man’s job was to pick up bodies at unkind hours, often under unkind circumstances. A woman running toward him in the dark was odd at best and dangerous at worst. But Bridge was getting desperate, and when she saw him, impulse took over. Maybe, just maybe, she thought, he could help.

“I want to work in forensics,” she told him. I’ve been struggling to find a way in.

“Do you have a business card?”

He decided to help her, and soon Bridge was shadowing the technician while he worked at the DC Office of the Chief Medical Examiner. It was an experience that led the young forensic chemist to jobs in the federal government, academic science, and the military.

Now an assistant professor of chemistry at the University of Central Florida, Bridge is in the middle of an ambitious, National Institute of Justice–funded project to chemically analyze sexual lubricants. She has built and is constantly adding to a database of molecular signatures that define different brands and formulations and show how these products break down over time.

In an era of rooms overflowing with untested rape kits, lubricant analysis could provide one more piece of evidence to tie someone to a crime. And in cases in which DNA is scant or a sexual predator has worn a condom, Bridge says the lubricant a rapist has left behind could be important evidence that keeps a sexual assault case from falling apart.

“I got a lot of phone calls from victims of sexual assault, telling some really terrible stories,” she says, recalling those days after getting her first, $324,000 grant from the National Institute of Justice (NIJ). Forensic scientists are supposed to be dispassionate, but the pain she heard in stories of dropped cases and bad evidence moved her.

“How this could be impactful for victims—it kind of made me, I don’t want to say cry, but it really did.”

She released the first iteration of the database in May.

Bridge is pursuing lubricant analysis for its potential forensic impact and for the sake of knowledge. Only a handful of labs worldwide do forensic lubricant analysis, yet the products represent a nearly $900 million market.

After basic ingredients—things like silicone polymers, poly(ethylene glycol), and the spermicide nonoxynol-9—manufacturers can choose from dozens of chemicals to create their signature products. Bridge lists a few: octylamine serves as an emulsifier, benzocaine lowers sensation, and any number of compounds work together to reduce friction.

Those chemicals become a sort of fingerprint of a sexual lubricant, she says. Through analytic chemistry tools like gas chromatography/mass spectrometry, Fourier transform infrared spectroscopy, and direct analysis in real time mass spectrometry, Bridge and her students can catalog the retention times and the telltale spikes that distinguish one lubricant from another.

At a crime scene, what makes a lubricant unique might also put a spotlight on a sexual predator.

For example, she says, there is only one lubricant they have identified so far that contains pulegone, which gives the product a raspberry scent. Police looking for a rapist could use this information to narrow their pool to only those suspects who have raspberry lube in their cars or houses. Or, she says, in a case of what looks like a string of unconnected assaults, identifying the same lubricant at each crime scene could be the key to connecting them, as serial offenders tend to be ritualistic and habitual when carrying out their crimes.

Lubricants will never be as definitive as DNA analysis in identifying individuals, she says, but with studies showing that between 15 and 30% of rapes involve condom use, everything the condom leaves behind, including lubricants, matters (J. Forensic Leg. Med. 2013, DOI: 10.1016/j.jflm.2013.03.023; Am. J. Men’s Health 2008, DOI: 10.1177/1557988308320008).

Since starting the project, Bridge has learned that manufacturers use silicone polymers of different lengths in their products. Her team is trying to figure out how to differentiate this common lubricant ingredient to be even more certain of what brand or type of lubricant someone uses in a sexual crime.

As she builds the database beyond what’s in different lubricants, she wants it to befit the complexity of what might happen in a sexual crime. For example, she’s investigating how vaginal and anal microbes can metabolize lubricants so that she can add such breakdown products to the database. And with a new grant from the NIJ totaling $354,000, her lab will examine lubricant composition from volunteers’ condoms after they have had consensual sex to see how it might change once it contacts human skin and other bodily fluids, and to measure breakdown products. Toward ending the backlog of untested rape kits, Bridge also wants to figure out how long a lubricant sample will last before it becomes too degraded to analyze.

To build this academic program, with two postdocs, nine graduate students, and six undergraduate students, Bridge has drawn from her experience working in crime labs, like the US Army’s Defense Forensic Science Center in Georgia. While she enjoyed that work, she says it was constraining—she wasn’t able to be creative or explore the kinds of questions she does as an academic. Those questions and research ideas have now become projects for her students and postdocs.

“I’ve basically put my whole career and tenure on the backs of condoms and lubricants,” she says, having begun the tenure process.

Running this large laboratory at the same institution where she got her PhD and did her postdoc, Bridge sees science, technology, engineering, and mathematics (STEM) recruitment as a significant part of her responsibilities at UCF. She knows that for many students, forensics is popular and approachable. Her introductory forensics class is routinely full at nearly 200 students, and almost every week, she says, a student will approach her to ask how to get more involved in the field.

But one thing troubles her, even as she runs a lab that is mostly women and incredibly diverse: women of color have been slow to take up the study of forensics.

“I always hear a lot of people say, ‘Oh, I would’ve always liked to do it, but I’m not strong in math,’ or whatever. There are hang-ups,” she says.

So in her free time, she works with school-age children to try to pique their interest in science. And she has a fairly open-door policy about what she does on campus: If you are interested in forensics, come see me. I will spend the time telling you about this field and what it takes to succeed.

She is the only black tenure-track faculty member in the Chemistry Department at UCF, and she recognizes that for many students on campus, she is not an example—she is the example.

Last year, at the National Organization for the Professional Advancement of Black Chemists and Chemical Engineers conference, she gave a keynote speech to the students in attendance.

Afterward, Bridge says, a young woman chased her down. She was a former student of Bridge’s at Howard University, where Bridge taught briefly after getting her PhD.

The woman told her, “I just want you to know that you are the reason why I went and pursued a PhD. You were the first black woman I had ever seen who was a scientist and a PhD. And because I saw you do it, I realized I could it myself.”