Slashdot Mirror
Dutch Cold Case Murder Solved After 8000 People Gave Their DNA
sciencewatcher writes "A 1999 cold case rape and murder in The Netherlands has been solved. Dutch police asked 8000+ men living within 5 kilometers of the crime scene to volunteer their DNA so that the murderer could be traced through (close or distant) family members sharing part of this DNA. As it turned out, the man now in custody turned in his own DNA, resulting in a 100% match. The request of the police was discussed here on Slashdot in September. The percentage of people participating was closing in on 90%; in the midsize town of the victim it was 96%."
The DNA matched DNA found on a cigarette lighter found in her schoolbag - not DNA from the rape itself apparently.
The DNA on the lighter matched DNA from the rape itself. The importance of the lighter is that it was sold during the time of the rape in that narrow area - placing the rapist as a resident of that area at the time, and giving high probability that a scan of all the residents would strongly indicate who the attacker was. If the lighter wasn't found, this search couldn't be justified as the rapist could come from anywhere.
It was more than a lighter exchange. Matching DNA was found on both the lighter and on the girl's body. That led to the DNA-dragnet. Apparently, the suspect's DNA matched the samples from her body and the lighter.
No, that's patently incorrect. The article (which I read, shame on me) makes it clear that the DNA on the cigarette lighter matches DNA present on the body of the victim:
The decision to launch the dna appeal came after De Vries in May broadcast information about a Playboy cigarette lighter found in Vaatstra's bag which contains dna traces that match the traces found on the schoolgirl's body.
More or less, they found DNA on her body, but had no immediate reason to suspect it was from someone nearby. When they found the same DNA on the cigarette lighter and were able to determine that the cigarette lighter was on sale in that area around the date that the rape/murder occurred, they thought they had reason to suspect a local individual was involved. That's what led to the DNA dragnet.
I do agree that police need to be careful with DNA evidence and not use it as proof of guilt where it implies no such thing, but that does not seem to be the case here.
The would be cool if they sequenced all the dna for comparison, but they don't. They look for specific markers that can actually be alike in unrelated people. A small chance, but not zero.
No, no, no, no, no! In a room of about 20 people there is a 50/50 chance of having two people with the same birthday. This is absolutely different of you having the same birthday as someone else, which is about 5.5% chance.
-- Pete.
Monochrome - Probably the UK's largest internet BBS
A regular DNA test has about 1/10000 success rate, but I would think that one can run a more thorough test (for a cost) that is much more precise than that. DNA doesn't have that collision rate.
That's the theoretical rate based on calculating the genetics of the population; it assumes that you run the scan perfectly. In fact labs make mistakes and cross contamination happens. This is something where the basic principle of science; actually do the experiment and see; must override the theory.
When people actually the lab error rate for genetic tests they get numbers like 1.7 in 1000 measured false positive rate. If you know a set of results where independent blind testing of the Dutch police DNA system has returned better results, please point to your peer reviewed study which shows so. I believe that most police labs aren't even subject to blind testing, so an even higher error rate should be expected.
=~ s,(.*),<sarcasm>$1</sarcasm>,g if any_point_you_wish();