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Concerning DNA testing in general. Recently there was a case where the Finnish police arrested a person as a suspect for a robbery of a convenience store on ba

Concerning DNA testing in general. Recently there was a case where the Finnish police arrested a person as a suspect for a robbery of a convenience store on basis of DNA evidence: the robber had dropped a plastic glove, presumably to hide fingerprints, on the floor of the store. Officers isolated DNA from the glove, searched archives, found a match with a person who had had some minor offense years prior, and brought him in for a questioning. It turned out the DNA-matched first suspect was innocent when the police found a second suspect, who confessed to the crime and whose clothes fitted security camera footage of the robbery better. So how the first suspect's DNA arrived on the gloves at the crime scene? The investigators noticed he told he had visited the same mall where the second suspect (according to his testimony) had obtained the gloves prior to the robbery. Based on the security camera footage from the mall, the investigators concluded that the likeliest way the DNA of the first suspect ended up on the gloves the robber because they rode the same escalator. Like this: https://images.cdn.yle.fi/image/upload//w_1200,h_1200,f_auto,fl_lossy,q_auto:eco/13-3-11824031.gif https://images.cdn.yle.fi/image/upload//w_1200,h_1200,f_auto... The lesson is, humans shed lot of skin cells around. The DNA from incriminating bodily fluids or similar is much better evidence than random DNA. Source https://yle.fi/uutiset/3-11811155 https://yle.fi/uutiset/3-11811155 and Google Translate: https://translate.google.com/translate?sl=auto&tl=en&u=https://yle.fi/uutiset/3-11811155 https://translate.google.com/translate?sl=auto&tl=en&u=https...

gherkinnn 5y ago
Or this woman: https://en.m.wikipedia.org/wiki/Phantom_of_Heilbronn https://en.m.wikipedia.org/wiki/Phantom_of_Heilbronn
barbazoo 5y ago
That's an adorably bad animation but it explains it perfectly
rhino369 5y ago
You need to apply Bayes Theorem to DNA evidence, but courts typically don't.
- beerandt 5y ago
  I'm not sure either prosecutors or defense attorneys would, in general, like the idea of basically forcing a jury to hear about percentages that they can't somewhat control via expert witness narrative. Or the idea of introducing most jurors to advanced statistics for the first time. I mean, even a lot of reasonably intelligent, college educated professionals that have taken a statistics class get lots of things very very wrong, very often.
  - rhino369 5y ago
    It would be the expert witnesses who would have to do the math--and they would reduce it down to a simple percentage chance. But now that I think about it, I bet defense counsel already does this. They did during the OJ trial.

gherkinnn 5y ago

Or this woman: https://en.m.wikipedia.org/wiki/Phantom_of_Heilbronn https://en.m.wikipedia.org/wiki/Phantom_of_Heilbronn

barbazoo 5y ago

That's an adorably bad animation but it explains it perfectly

rhino369 5y ago

You need to apply Bayes Theorem to DNA evidence, but courts typically don't.

beerandt 5y ago
I'm not sure either prosecutors or defense attorneys would, in general, like the idea of basically forcing a jury to hear about percentages that they can't somewhat control via expert witness narrative. Or the idea of introducing most jurors to advanced statistics for the first time. I mean, even a lot of reasonably intelligent, college educated professionals that have taken a statistics class get lots of things very very wrong, very often.
- rhino369 5y ago
  It would be the expert witnesses who would have to do the math--and they would reduce it down to a simple percentage chance. But now that I think about it, I bet defense counsel already does this. They did during the OJ trial.