Modern Forensic Science And the Danger of Contamination
April 14th, 2009
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One of the most effective weapons in fighting crimes where no witnesses exist but physical evidence remains. Especially in cases of rape, DNA analysis can turn a cold case into a shut case and a slam dunk for conviction. The techniques of DNA fingerprinting have come a long way. Modern PCR systems can replicate DNA from samples so small they’re invisible. In the past, a DNA match required a relatively significant amount of blood, semen or tissue. Today, a swab containing a few cells can generate a profile that can lead to a perpetrator, exonerate a suspect or confirm a connection between crimes.
There’s another side to this technology, however. With so little material required, contamination becomes a greater concern than ever. That seems to be what happened in Germany, where a series of apparently unrelated murders were linked by the same DNA found at the scenes at the crimes. These murders happened in different areas and had different MO’s, but with common DNA, Authorities believed they had a serial killer. Further testing indicated that their killer was a woman.
But now it seems, there may not have been a serial killer after all…
The murderer dubbed the Phantom of Heilbronn had been baffling German investigators for two years. The criminal was a rarity, a female serial killer, and a very busy one: police had linked DNA evidence from 40 crimes — including the infamous homicide of a policewoman in the southern German town of Heilbronn — to the same woman.
olice had found her DNA on items ranging from a cookie to a heroin syringe to a stolen car. They had put a $400,000 reward on her head. Profilers from around Europe were called in to help hunt her down. The police even consulted diviners and fortune-tellers in hopes of discovering her identity. The papers declared the case “the most mysterious serial crime of the past century.”
The police thought they’d been looking everywhere. But it turns out they should have been looking down — at the cotton swabs they were using to collect DNA samples. On March 26, German police revealed that the cotton swabs they use may have all been contaminated by the same worker at a factory in Austria — and that the Phantom of Heilbronn never existed.
An amazing and very unsettling story. With tests as sensative as they are today, a worker misshandling cotton swabs at the factory can contaminate samples and produce prositive readings with just a few skin cells. Contamination is an enormous concern because crimes do not happen in steril laboratories and therefore, even if cotton swabs are not contaminated at the time of manufacture, they could easily pick up DNA that is unrelated to the crime from any number of sources.
Is it possible that sitting on a bus in a seat later occupied by someone who would be murdered later that day could lead to a person’s DNA ending up on sample swabs? What about having sneezed in the area a day before the crime occured? These are things we’re increasingly going to have to consider, especially as more states and countries establish DNA databases of all those arrested. A person could be arrested for an unpaid parking ticket and end up being accused of murder if such contamination were to occure.
There is at least one intriguing and bizarre story of a conviction stemming from a microscopic DNA sample:
In 1969, Jane Mixer Michigan was found dead in a cemetery near Ann Arbor. Thirty six years later, investigators attempted to extract DNA from the evidence archived from the crime. There were two potential source, a small drop of blood found on the victim’s hand and a DNA which was extracted from the victims stockings. The DNA from the stockings was minuscule in quantity – so small the source material could not be identified – it could have been sweat, saliva or even tears, but it was not from Mixer.
Two distinct DNA profiles were developed, one from the stockings and the other from the spot of blood. Both turned out to be in the database of arrests in the state. The drop of blood, which had been swabbed from the victim’s hand matched a convicted killer who was already in prison and smudge from her stockings matched a man who had been arested on drug charges after he became addicted to pain killers. The individual in question didn’t have any convictions (charges were dropped as part of an agreement to get treatment) and he had history of violence.
It would seem that the obvious suspect of the two would be the convicted killer, a John Rueles. But at the time of the murder, Rueles was only four years old. He also lived on the other side of the state. Thus, Gary Leiterman, the individual whose dna was matched to the sample on the victims stockings was arrested, tried and convicted. To be fair, there is some circumstantial evidence that Gary Leiterman may have been in the same area and may have owned a gun similar to that used in the murder, but the state never explained how the other DNA could have ended up on the victim.
Rueles himself could offer no explaination or memory from his childhood to explain how his blood could end up on a murder victim. Detectives investigated his uncles, who he had lived with at the time along with other family members but could find no connection to the crime. The prosecutor admits that the source of the DNA remains a mystery but rebuffed claims of contamiantion.
Leiterman’s trial, which is now underway in state circuit court here, would likely have been a fairly straightforward proceeding if the smudges on Jane Mixer’s pantyhose were the only evidence the lab turned up.
…..
He owned a .22-caliber gun, the same caliber that killed Mixer, and his roommate at the time remembered him collecting news articles about a string of murders of young women in the area. He also bragged to the same man that he had drugs that could render a woman unconscious or even kill her.
What is chilling is simply considering the fact that Rueles would have almost certainly been charged with this crime if he had been born ten or more years earlier. Whether or not Gary Leiterman is guilty, I really don’t know. The additional testemony of his habits and the weapon he owned does add weight to the case, but in the end, there’s a good reason to be concerned about cases hinging on such tiny samples that can so easily be contaminated.
I guess it might be best if I turn down any job offers from cotton swab factories..
This entry was posted on Tuesday, April 14th, 2009 at 2:24 am and is filed under Bad Science, Good Science, History, Misc. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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April 14th, 2009 at 2:36 am
The sensitivity of these tests does not even require contamination of the samples. As you say, someone could sneeze or something and it could end up on the victim. Perhaps sit on the same seat when you’re sweaty or something? If there’s significant fluid of some kind that’s one thing. It’s just important that investigators consider all the possibilities. Forensic technology is no magic bullet. Some juries think it is though. All things need to be viewed with appropriate skepticism and open mindedness.
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April 14th, 2009 at 3:24 am
Q said:
We all owe the CSI franchise a debt of thanks for that.
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April 14th, 2009 at 4:58 am
My DNA (and prints) are known to the police after I was arrested for the unspeakable crime of throwing an unwanted guest out of my house (yes, yes I know – I should have just rolled over and taken it but that’s an argument for another time). Being swabbed for samples has always rankled as I was never actually charged in the end.
I often wonder what crime CSI will eventually find I have committed.
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April 14th, 2009 at 10:48 am
I hope thorough psych profiles are done on those cotton swab factory workers. Those with a vindictive streak might find it difficult to resist the temptation.
I know I would.
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April 14th, 2009 at 12:11 pm
While DNA evidence has its problems, it is still far better and more reliable than eye witnesses.
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April 14th, 2009 at 12:27 pm
DNA evidence, is also easy for police to manipulate by introducing DNA and using questionable testing procedures.
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April 14th, 2009 at 1:23 pm
Chuck said:
Oh god yes.
Bruce said:
there are procedures to try to avoid that. The cops who handle the evidence are not the same people who collect the samples from suspect and they’re independently tested and everything. Still, it’s always something worth considering in any case.
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April 15th, 2009 at 11:23 am
I read about the case of Gary Leiterman and based on the evidence I think he is *probably* guilty, but if I were on the jury I would have had a lot of trouble convicting him. Just too much reasonable doubt. The whole thing with a microscopic sample is that there could be an alternate explaination for how it might have gotten on someone, even if not contaminated. He could have hocked a loogie onto a park bench or something, if he lived in the same area.
DNA alone doesn’t mean someone should be convicted. It means that the person was there or that they crossed paths with the victim or something. It doesn’t mean that they committed the crime. That’s what has to be proven is that there is no other way the dna could have gotten there.
It’s like finger prints. If a finger print is found in the bathroom of a house where someone is killed and that fingerprint belongs to a plumber who had fixed a leak a few days before it certainly does not mean that they killed the person. If it belongs to someone who never had reason to be there though, then it’s more suspicious.
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April 15th, 2009 at 12:54 pm
I wonder if the polizei came down on the Austrian q-tip worker like a ton of bricks, only later finding out the real reason why her DNA was on 40 murders? That could be a terrifying ordeal. One false move and they blow her away… Or did they figure out who she was by eventually considering the contamination angle, and checking the swab factory workers?
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April 15th, 2009 at 2:32 pm
I read somewhere that they began to suspect contamination a while ago but they knew something was a miss when they found the same DNA result on swabs relating to an unknown male corpse. They were trying to identify a body from a fire so they tried to recover DNA from items that belonged to individuals who were missing in order to compare them to the corpse. I don’t know the details but I know sometimes they do that with toothbrushes or something to try to identify remains.
Anyways, when the result started showing up as a hit to this female serial killer, they knew for sure something was up.
Sorry, I don’t have the link for that and I may have gotten a couple of details wrong, because this was about a week or two ago that I saw it. Apologies for just my hazy recollection on this.
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April 16th, 2009 at 1:32 am
As I recall there has been some suspicion around this for some time.
Worst part might be that if the police were convinced they had a serial murdered on their hands and one crime was related to another then they may have turned a blind eye to potentially useful leads which have since gone cold. I bet a few killers got lucky on this blunder.
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April 16th, 2009 at 1:44 am
Cell line cross-contamination can be a problem for scientists working with cultured cells as well. Studies suggest that anywhere from 15–20% of the time, cells used in experiments have been misidentified or contaminated with another cell line. Because of their avid adaptation to growth in tissue culture plates, HeLa cells are one of the worst and most persistent laboratory “weed” and they can contaminate other cell cultures in the same laboratory, interfering with biological research, and forcing researchers to declare many research results invalid because the cells used were found afterwards to be contaminated
The immortal HeLa cell line was derived from cervical cancer cells taken from Henrietta Lacks, who died from her cancer, and were derived for use in cancer research.
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April 16th, 2009 at 3:05 am
Question that is off topic: If I understand correctly, the HeLa cells are from a woman in the 1950’s whose cancer was used to culture cells for research and now the cells have adapted by their own evolution to be especially good at living in artificial culture so that they can invade other cell cultures in the same lab or area.
If that is the case, why not just stop using the HeLa cell line? Surely there are other people around who an have their tumor used for some research cells. If a laboratory never uses the cells and doesn’t trade cultures with labs that do then it would seem like it minimizes the chances.
Also, if they’ve adapted so much then are they even still worthy subjects of in vitro research?
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April 16th, 2009 at 3:55 am
Magic Donuts said:
There are many strains of HeLa cells as they continue to evolve by being grown in cell cultures, the problem is that they have already contaminated over forty other cell lines so they are not that easy to get rid of, or avoid.
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April 19th, 2009 at 7:37 am
It looks like the HeLa is an infection of sorts whose natural carrier is the genetic biologist
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April 26th, 2009 at 11:05 am
DNA is important, as important as fingerprints as a development in crime science. DNA can be amazingly effective in some cases and especially rape, because forign semen on a rape kit is a slam dunk for good dna of the rapist. There is still the issue of putting it in context though. One can’t take it alone and needs to ask the questions like could it have gotten there by another means or is there another explanation like bad collection etc.
There is another disturbing side to this called the CSI effect. Juries are known to put so much weight on forensic evidence it becomes a trump card to convict even when other evidence indicates there could be an issue with it. “His dna was there. He must be guilty.” Also, juries now expect forensic evidence. That is very bad because most cases are not built on forensics. Most cases no readable prints or collectible dna is there. Juries want that now and think it *should* be there.
Blame OJ Simpson case. Blame the news media. Blame CSI. Whatever, it’s a problem. I like to blame CSI because it’s a stupid show to begin with.
Being on a Jury does not mean being a slueth. You just listen to both sides objectively and try to see what makes sense and whether it is proven. It is a serious duty that people need to take seriously.
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November 8th, 2011 at 12:22 pm
Forensic science has a very high profile on TV and across the media in general. This profile includes both real world references to forensic science in such programs as The First 48, and fictional references to forensic science most notably in shows such as CSI, CSI Miami etc.
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