What if the biological evidence disproves the crime?


photo credit: jared via photopin cc
photo credit: jared via photopin cc

In honor of the fact I’m doing some forensic DNA consulting, I’m allowing people to pick my brain about real-life forensic science. Simply ask your question in the comments, and I’ll either answer it there, or expand in a blog post. We’ll go as long as you guys have an interest.

The question for today was submitted by Loraine Kemp, a fantastic writer and illustrator. She wants to know,

Did you ever have to report on a case where the evidence was presented to you/the lab with a story of what had happened in the crime scene and you had to disagree based upon your findings?

The short answer is, yes. That happens pretty often. If you’re a good forensic scientist (one that is not biased), you don’t have a vested interest in the outcome of a case. It’s your job to analyze the evidence to the best of your ability, and then report those findings back to law enforcement to help them do their job. The great thing about DNA is that while it is a powerful tool that can be used to link people to a crime scene, it is equally powerful in exonerating individuals who are under suspicion.

Let’s say that a woman was attacked by an acquaintance. Maybe she had just met him and was at his apartment. She manages to get away after he falls asleep by taking his keys and leaving in his car. She reports the assault (or attempted assault) to the police. Maybe she goes to the hospital and they collect her clothing and biological evidence from her body to submit to the lab.

What happens if the man (now a suspect) calls the police department to report his car stolen?

What happens if law enforcement finds out that this woman has made multiple claims of being attacked by different men and taking their cars as a means of escape? Or that she claims she was assaulted to cover up her serial joyriding fetish?

Let’s say that a certain biological fluid was found on the woman’s shirt by the laboratory (use your imagination, I’m trying to be PG here). If the biological fluid was consistent with the DNA of the man, what would that tell you? Would that mean she had been assaulted by him? Or might it mean that they engaged in some mutually consensual activities before she stole his car?

What if the DNA results showed that the biological fluid was NOT from the man with the car? Would that mean that he didn’t assault her? What if there were multiple stains on the woman’s shirt, and each produced a different male profile, neither consistent with our alleged attacker? What would you think then?

photo credit: LauraLewis23 via photopin cc
photo credit: LauraLewis23 via photopin cc

Hopefully you see the point I’m trying to make. There are two sides to every story. Complainants don’t always tell the truth. Maybe they’re embarrassed about what happened. Maybe they’re mad at an ex-boyfriend and want to try to get him in trouble. Maybe they’re trying to divert attention from their own illegal activity. Or maybe they’re underage and brought to the hospital by a concerned parent. You never know.

The best thing to do is analyze the evidence you have and report the results you get. Forensic scientist don’t determine guilt or innocence; that’s the purview of the jury should the case get that far.





9 thoughts on “What if the biological evidence disproves the crime?

  1. I can definitely see what you mean. I remember hearing about just such a case a few months ago – so many conflicting stories and I’m not sure they ever did get it really figured out. The case was eventually settled. I can see why your critique partners are clamoring for you to write murder mysteries and such. That’s the neat thing about fiction – all those nuances can be explored.


    1. If I wrote a murder mystery, I would have to put it in the future as a dystopian or in some made up realm. Maybe a cool urban fantasy? I’ve been thinking about writing one and using all my writing buddies as characters. Wouldn’t that be fun? 😉


      1. That would be fun because then you wouldn’t be limited except by the scope of your imagination! haha – just don’t kill any writing buddies! Did you watch any Almost Human? (Just googled it – it got canceled!! Of course, it got canceled, my husband and I actually liked it. That was it’s death nail…) Anyway, it was set in a unique, possibly-dystopian future and had some interesting possibilities technology-wise.


              1. Oh gee – anything is fine. You can even kill me off, if you want. Just make me something as unstereotypical as possible? I love characters that go against the norm; people who are the opposite of what you expect from the surface appearance.


  2. Thanks for answering my question Lisa! I amazes me with the technology available now that someone would make up a story and try to get away with it. Come on! Really? Don’t they watch CSI? This isn’t the 1800’s… One more question, if I could… how long was the course to become a forensic scientist?


    1. Technology has its limits. Finding a DNA profile or fingerprint or whatever is only as good as the item of evidence it’s on. If you find a fingerprint or DNA profile at the home of a burglary but it belongs to one of the residents or a friend, it’s not necessarily helpful. But finding a DNA profile on a spoon left after the burglar ate cottage cheese during the burglary – now that IS helpful (and really did happen).

      To answer your course question, to work in an accredited lab, each discipline has their specific requirements (toxicology, drug chemistry, trace evidence, forensic biology/DNA, etc.). Generally, a person has to have a bachelors degree in some sort of science. For DNA, a person also has to have specific courses such as molecular biology, genetics, biochemistry, and statistics/population genetics. Once you’re hired, you have to go through a training regimen (minimum of 6 months to interpret DNA profiles). Of all the forensic science disciplines, DNA has the most specific requirements.

      So anyone with a strong science background has the coursework to become a forensic scientist. People can also get degrees in forensic science in some colleges now. Our laboratory had a nice mix of forensic science and pure science grads.


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