There was a serial killer roaming about the German foothills.
DNA from the same person – a woman – was linked to 39 different crime scenes and 7 murders throughout Germany.
According to scientific literature, the odds of finding an exact DNA match between unrelated people is 1 in 1 quadrillion. For those of you who have been desensitized by the “illion” factor in the recent rounds of government spending, one quadrillion is 1000 trillion or 1,000,000 billion or 1,000,000,000 million or just plain 1,000,000,000,000,000
Since there are only 400 million people in the United States, if a DNA “match” is found at a crime scene in this country, it’s likely that a defendant is guilty until proven innocent. DNA analysis involves examining 13 alleles from evidence samples and from suspects. If 9 of those sites are the same between samples, they are considered a “match.” Here is a more in-depth Wiki about “genetic fingerprinting.”
DNA evidence may not be as reliable as prosecutors would have you believe, though.
In this article from the LA Times, a database of 30,000 DNA profiles contained 32 “matches” at 9 of 13 loci and three “perfect” matches at 13 of 13 loci. Another search of 6 million DNA profiles from two states found more than 1,000 matches at 9 of 13 loci (article is fascinating read if you’re into DNA evidence).
When the German serial killer’s DNA was found at the scene of a murdered 22-year-old police woman, the stakes changed. A 300,000 euro reward was offered for information leading to the killer’s arrest. Police released a sketch of a man they thought might be the killer, hypothesizing that the killer was a transsexual. Eight hundred female criminals were interrogated. Thousands of saliva tests were taken. No luck.
A hunch by a veteran detective helped crack the case.
The woman whose DNA was linked to so many crimes and murders lived quietly amongst her neighbors, cooked dinners for her family at night, but by day …
she worked in the factory that made the cotton swabs used to obtain the DNA specimens from the crime scenes.
Contaminated specimen swabs, not a serial killer, were to blame for the DNA matches.
See news stories here and here.
And now you know … the rest of the story.
I miss Paul Harvey.
Hat tip to Overlawyered for the link.
Very interesting. Guess she should be wearing gloves!
Incredible! This puts a whole new twist on “reasonable doubt” — both of guilt and innocence. Great post.
Thumbs up for missing Paul Harvey.
This statement: “if a DNA “match” is found at a crime scene in this country, it’s likely that a defendant is guilty until proven innocent” is not quite accurate.
In fact, mathematicians call it the “prosecutor’s fallacy.” That is, the probability that a given DNA sample matches a given person (and only that person) are not the same as the probability that that person committed the crime. That has to be demonstrated by other means. Merely having been at a crime scene is not, by itself, proof of guilt, though it certainly is something a defendant must have a pretty darn good explanation for.
I was wondering how the info/story that you posted above might influence your reaction to this story in today’s NYT:
http://www.nytimes.com/2009/04/19/us/19DNA.html
“Law enforcement officials are vastly expanding their collection of DNA to include millions more people who have been arrested or detained but not yet convicted. The move, intended to help solve more crimes, is raising concerns about the privacy of petty offenders and people who are presumed innocent….”