Just as an FYI for those of us discussing DNA from semen, my husband who has 17 years experience as a detective said that a body left in the elements for 30 days will likely *not* have any retrievable DNA from the vagina. BUT... that it is all dependent on the decomposition process of the individual victim and each victim decomposes in their own way even though the basics of decomposition are the same. So, it is possible to find evidence of a sexual assault after 30 days but would be highly unlikely. He said typically in that situation, they take samples from the entire body and “hope for the best.”
As for fingernails, he said in his opinion and experience, DNA can be found under the fingernails for quite a while and he said he believes at 30 days post death there would be a good chance of recovering DNA from fingernails.
- just my opinion. Actually, my husband’s opinion... but same difference