Innocent Man Charged With Murder Because His DNA Was Found On The Fingernails Of Victim, Whom He Had Never Met

from the DNA-is-formidable,-not-infallible dept

The forensic use of DNA is rightly regarded as one of the most reliable ways of establishing the identity of someone who was present at a crime scene. As technology has advanced, it is possible to use extremely small traces of genetic material to identify people. One possibility that has so far received little attention is that the DNA of someone might be transferred accidentally to a murder victim’s body, say, even though the former person had absolutely nothing to do with the latter’s death, and maybe had never even met him or her. The Marshall Project has a fascinating and important report on just such a case.

Back in 2012, a group of men broke into the Silicon Valley home of a 66-year-old investor, tied him up, blindfolded him, and gagged him with duct tape. The duct tape caused him to suffocate, turning a robbery into a murder. Some DNA found on the victim’s fingernails matched that of a homeless man, who was well-known to local police. It seemed an open-and-shut case — even the alleged murderer, who had memory problems, admitted he might have done it, given this apparently incontrovertible proof. Fortunately, his lawyer was diligent in checking everything about her client in the hope of at least mitigating his punishment. As she examined his medical records, she discovered the following:

The medical records showed that [the accused] Anderson was also a regular in county hospitals. Most recently, he had arrived in an ambulance to Valley Medical Center, where he was declared inebriated nearly to the point of unconsciousness. Blood alcohol tests indicated he had consumed the equivalent of 21 beers. He spent the night detoxing. The next morning he was discharged, somewhat more sober.

That night her client had been in hospital was when the murder had been committed. Further research confirmed that he could not have been on the crime scene, and also that he had never met the victim. The question then became: how had his DNA — for there was no doubt it was his — ended up on the fingernails of a murdered man?

The connection was found in the paramedics who had responded to the discovery of the murder victim. It turned out that earlier that day they had taken the innocent man accused of the murder to Valley Medical Center after he had collapsed drunk in a supermarket. Somehow, improbable as it might seem, they had transferred his DNA onto the murder victim, where it was later discovered by the forensic scientists.

The Marshall Project article goes into much more detail about the case and the history of using DNA to solve crimes — it’s well-worth reading. It highlights two crucial facts that need to be taken into account when DNA is used as evidence, especially for serious crimes carrying heavy penalties. One is that we all leave our DNA everywhere:

An average person may shed upward of 50 million skin cells a day. Attorney Erin Murphy, author of “Inside the Cell,” a book about forensic DNA, has calculated that in two minutes the average person sheds enough skin cells to cover a football field. We also spew saliva, which is packed with DNA. If we stand still and talk for 30 seconds, our DNA may be found more than a yard away. With a forceful sneeze, it might land on a nearby wall.

To find out the prevalence of DNA in the world, a group of Dutch researchers tested 105 public items — escalator rails, public toilet door handles, shopping basket handles, coins. Ninety-one percent bore human DNA, sometimes from half a dozen people. Even items intimate to us — the armpits of our shirts, say — can bear other people’s DNA, they found.

The other fact is that contamination of key DNA samples by those investigating a crime is the rule, not the exception:

A 2016 study by Gill, the British forensic researcher, found DNA on three-quarters of crime scene tools he tested, including cameras, measuring tapes, and gloves. Those items can pick up DNA at one scene and move it to the next.

Once it arrives in the lab, the risk continues: One set of researchers found stray DNA in even the cleanest parts of their lab. Worried that the very case files they worked on could be a source of contamination, they tested 20. Seventy-five percent held the DNA of people who hadn’t handled the file.

As the article emphasizes, DNA is indeed an incredibly powerful forensic tool, which has helped convict the guilty, as well as exonerate the innocent. But it is not infallible. The question is: how many other people have been wrongly charged, convicted and punished because of stray DNA?

Follow me @glynmoody on Twitter or, and +glynmoody on Google+.

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Comments on “Innocent Man Charged With Murder Because His DNA Was Found On The Fingernails Of Victim, Whom He Had Never Met”

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Roger Strong (profile) says:

I did my first programming with punch cards, back when it was still common to hear the claim "Computers don’t make mistakes!"

Despite the astronomically high improbabilities claimed for false DNA matches, gosh, I hear of a lot of false matches. They’re for much the same reasons as computers: Procedural errors at the lab. Data entry errors. And just plain bad data.

That includes the Phantom of Heilbronn: An unknown female serial killer whose existence was inferred from DNA evidence found at numerous crime scenes in Austria, France and Germany from 1993 to 2009.

Investigators later concluded that the DNA belonged to a woman who worked at the factory where the cotton swabs used at all the crime scenes were made.

Anonymous Coward says:

Re: Re:

Most DNA samples, like most fingerprints, are only partials. You get to see a little bit of it and make your best estimate of the chances that it matches a known DNA or fingerprint. What would make DNA evidence fairer would be a report to the jury of how complete the sample was and, if incomplete, how much that changed the probability of a correct identification. Good luck explaining that to the average juror. They don’t understand probabilities.

The case above involves an entirely different problem. So-called professionals, including paramedics and lab analysts, are routinely sloppy in transferring DNA from one person to another. Better training and procedures would help, but jurisprudence has always been a hit-or-miss affair and only in Wonderland will it ever be different.

Anonymous Coward says:

Minimum amount

There seem to be issues with the types of tests used as well but leaving that aside maybe minimum standards?
On the nail is not the same as skin found under the nail from scratching and resistance. We can extract DNA from very very very very very very tiny samples so maybe we need a minimum amount of DNA present to ensure it is not accidental or environmental transfer?

That Anonymous Coward (profile) says:

In their rush to see if they could do it, they never asked should they do it….

DNA from blood, semen, saliva is really hard to claim came from someone else or was planted.

Touch DNA, even the Dr. (iirc) who was involved in showing how it worked said it can’t be the be all end all because everyone sheds.

DNA is just magic these days.
If they find yours, the jury knows you did it.
If they finally test yours, you get off of death row.

No one has explained how everyone sheds cells differently & how in testing they showed items never touched by a subject having their DNA on it from others being in the same area.

Everyone wanted a tool that could take the tiniest scrap of DNA and show us the murderer before the 2nd commercial break.

The problem is that many times the investigation stops once the DNA matches, thankfully for this man he had an airtight alibi once they were willing to look at it.
Everything they imagined up until that point about his involvement would have convicted him & been taken as truth.

Tools are just tools, not perfect magic.
They can be misused & abused, we can not allow people to think the science is perfect. Look at all of the labs having to toss convictions b/c they finally decided maybe they should look at their labs & notice the missing drugs not to mention one person doing testing at like 7x the rate of other top labs.

Marienne Branch says:

Re: Reasonable Doubt

Last I heard fingerprints are no longer infallible & not necessarily unique to each of us. Remember when eyewitness testimony was the old DNA? They’ve (prosecutors, judges & the like) finally acknowledged the truth that everyone else has known for a long time – it is possibly the most unreliable evidence ever – considering how many innocent people have been locked up or worse based on it.

Lawrence D’Oliveiro says:

Re: Re: Last I heard fingerprints are no longer infallible

They never were. It’s just they became popular back in an era where the science of statistics was not so well-developed. DNA analysis has had to weather sophisticated statistical scrutiny since its beginnings, which you would think would have made it stronger. The trouble is, people have very poor intuitions about probabilities, and the logic of probabilistic arguments can get very subtle. This includes the cops themselves, not just juries.

Marienne Branch says:

The Fallibility of DNA

As I read this frightening & enlightening article I kept thinking that there’d be a mention of chimaerism in humans. I found out about this possibility in humans watching a television show, to my best recollection, about a mother who, when giving blood in a parternity case was declared not the mother of her child/ren. As you can imagine, her life went to hell! She was restored to her family, life as she knew it & sanity when her blood was taken from another part of her body for reasons unrelated to the maternity issues (If I remember correctly.) & her chimerism was discovered and, in time, her life returned to normal. While this was new information to me, the story didn’t seem to treat it as a revelation – yet, I’ve not seen it referred to again – no matter how many true crime television shows I watch & books I read. Et tu, Brutus?

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