Re:Yet another scientific body has debunked bitemark analysis
by tsimionescu on Friday October 21, 2022 @02:09AM
(#33285034)
There is some amount of the science itself being inconclusive, as no one has really studied things like "how likely is it for DNA that matches X's to n% precision to be in a location Y given that X has/has not visited that location".
Even discounting intentional placement of evidence, we really don't know how likely it is to find pieces of your DNA in places near to those you frequent - say, in the lobby or elevator or first floor of an apartment building you pass by every day, but have never entered. This is especially important given partial matches, since it's likely thousands of people pass by a building each day that have never made it inside - so the chances of an accidental match increase greatly (while also being guaranteed to match corroborating evidence, such as security cameras seeing you next to that building on the day of).
Conversely, we also don't know how likely it is that you can avoid leaving your DNA in a place you have visited to commit a crime.
Now sure, there are cases like "we found a large smear of blood, all of it containing DNA that matches this suspect 99%, and the suspect has an obvious open wound/scab"; or, the same smear containing DNA that only weakly matches the suspect or the victim or any known eye witness, which is extremly good evidence that someone else was at the scene.
But when one hair or bit of spit is found in an apartment that matches someone who does live around that area, we don't really know if that means anything.
Even discounting intentional placement of evidence, we really don't know how likely it is to find pieces of your DNA in places near to those you frequent - say, in the lobby or elevator or first floor of an apartment building you pass by every day, but have never entered. This is especially important given partial matches, since it's likely thousands of people pass by a building each day that have never made it inside - so the chances of an accidental match increase greatly (while also being guaranteed to match corroborating evidence, such as security cameras seeing you next to that building on the day of).
Conversely, we also don't know how likely it is that you can avoid leaving your DNA in a place you have visited to commit a crime.
Now sure, there are cases like "we found a large smear of blood, all of it containing DNA that matches this suspect 99%, and the suspect has an obvious open wound/scab"; or, the same smear containing DNA that only weakly matches the suspect or the victim or any known eye witness, which is extremly good evidence that someone else was at the scene.
But when one hair or bit of spit is found in an apartment that matches someone who does live around that area, we don't really know if that means anything.