Gnu,

Assume that you have a DNA sample from an unknown assailant and further assume that DNA testing shows that "approximately 85,000 other people in the US could have" left the DNA in question. Given the population, that is the same as saying that there is roughly one chance in 4000 chance that an INNOCENT person picked randomly would match that DNA. Which is to say that, about 3,999 times out of 4000, the DNA of an innocent person picked randomly would NOT match.

If there were no other evidence EXCEPT the DNA, such evidence would not be sufficient to convict. Suppose, however, that based on other evidence, you already suspected X was the assailant. Based on this suspicion, you test X's DNA. If you find a match, the odds are increased that X is really the assailant. Exactly what those odds are depends on the other evidence.

Hope this helps.


Kent