By Carissa Horst

“I have gotten the reaction before: ‘So . . . I shouldn’t commit any crimes around you.’ I’m like, ‘You're right, mostly because you shouldn’t commit crimes, but yeah, I’ll catch you, so don’t do it. I know where to look for your DNA.’”

Scaring your friends away from breaking the law is one advantage of working in forensics (forensics is using science to uncover crime)—but there are many other unusual aspects to it. For forensic DNA analyst Sarah Yearsley, the job is both exciting and intriguing. As part of her job, she is involved in everything from highly-sensitive lab work, to crime convictions, and at one point, overseas military operations. Out of graduate school, Yearsley began at the U.S. Army Defense Forensic Science Center. She spent most of her time in the U.S., processing samples from around the country and different parts of the world. But her favorite memories in that position stem from her two deployments to Afghanistan. “I absolutely love the experience of deploying,” she said. “I love living out on the base; you work 12 hours a day every day of the week.” She provided an example of what she worked with: “...someone’s attacking the base with mortars or rocket attacks and [our soldiers] find the launch site and find a cigarette butt on the ground there. They’re able to send that to us and we process it and it [matches] someone that lives in a ten-mile radius. Now we’re able to find the person who’s directly attacking U.S. soldiers and civilians.”

Though it was an intense time, Yearsley discovered that it meant a lot: “Being out there is such an awesome experience; you feel like you’re really making a difference, because you are—these guys are putting their lives on the line to collect stuff and bring it to us.

When we’re able to give them good results that can provide intel or additional leads for them, it makes a big difference.”

Landing a job back in the States, Yearsley remembers giving her first testimony in court. The case surrounded a man suspected of planting a pipe bomb on his ex-girlfriend’s doorstep, though the bomb was only detonated by the police after it was discovered, without causing any harm. Sarah and her team found the same complete DNA profile on everything—the wires, tape, box, batteries, and bag—and it matched the suspect’s. “When you have a complete profile, the statistics can be really, really high,” Yearsley explained. “The chance of finding this profile in an unrelated individual in the population is one in thirty quadrillion or something. The numbers get really, really high because DNA is so individualizing.” Yearsley testified in court, supporting the prosecution to make a very strong case. The man was convicted.

Yearsley described her role as a professional witness: “You can’t be biased as an investigator, you just give the stats as they are, and no matter what hypothetical the defense comes up with, you gotta be like, ‘Yes that’s possible, but unlikely for these reasons.’ You have to stick with the science and remain unbiased, but in this case, his DNA was all over everything.”

Media paints the field of forensics as brimming with sky-high stakes and life-and-death investigations. While this is sometimes the case, that does not always reflect the day-to-day scene of the job.

Yearsley spends most of her time in the lab, where she receives evidence, either grouped with a specific case or individual and unrelated. The evidence could be anything from firearms to arson-related weapons and explosives. She swabs the object in a high-contact area (ie. the trigger of a gun) or cuts it out and places it in a tube to process. The goal is to obtain as complete a DNA profile as possible without it being contaminated by other DNA.

“It’s grown from where you originally needed a quarter-sized spot of blood to do any sort of processing, to now, we will process a single fingerprint.” The method of processing DNA from the skin cells in a fingerprint or two is called “touch DNA,” and it means that evidence is very susceptible to contamination. “In the lab I’m like: lab coat, gloves, sleeves, another pair of gloves, I wear a mask, hair nets, and safety goggles. We look like science-y lunch ladies with our hair nets, but it works.”

Once Yearsley has a DNA profile, she writes a report, then uploads the profile to a database—in the U.S. it’s CODIS (Combined DNA Index System), which contains the DNA of anyone who has committed a crime and had their DNA processed.

To begin her career as a forensic DNA Analyst, Yearsley obtained her bachelor’s degree in Biology, then her master’s in Forensic Science. However, to anyone who is interested in the field of forensics, any undergraduate science major such as biology, micro-biology, or chemistry is a good start.

Yearsley reflected, “I was very unaware [of what this job would be like] when I was in high school and I decided this was what I wanted to do, [. . . but] I’m glad I stuck with it, because I love my job.”

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