In the last few years, law enforcement has begun to cash in on modern genetic technology in a new and more powerful way, one that works on perps that have been careful enough to avoid being genotyped.
The perp’s DNA sample is matched against a large database of genome sequences, and if a moderately long subsequence is identical-by-descent, it’s clear that the perp and the matching person in the database share fairly recent common ancestry. The degree of sharing shows, approximately, how recent that common ancestry is.
This has been done for some time with close relatives, which share up to 50% of their DNA. But by now, enough people have been genotyped that there’s a pretty good chance that the typical perp ( of European ancestry) has some moderately distant match in the database: say, a 3rd cousin. We can now detect those matches. A few such matches tells us that the unknown perp is one of the descendants of an ancestor a few generations back – so we now only have to examine a very limited pool of potential perps, perhaps a few hundred instead of tens of millions! After excluding individuals of the wrong sex, impossible ages, deceased, etc finding the real killer often becomes quite practical.
In particular, enough people have been genotyped and have uploaded their info to a genetic genealogy site to allow this. I said of European descent: genotyping and interest in genealogy have not as yet been widespread enough among African-Americans to allow this approach , but that will come, probably fairly soon.
What this means, to a pretty good approximation, is that law enforcement is soon going be able to identify the perp in all cases where DNA evidence is available. Decades of unsolved rapes, assaults, and murders will be cleared up – in as little as a couple of years, if we make a serious effort.
Exceptions? DNA from your evil twin, and DNA from truly obscure groups with no representatives in the US. People will write murder mysteries featuring Andaman Islanders -they’ll have to.
We will not find that all or most prominent people have a criminal past ( I think) – but quite a few will, undoubtedly including people you would never have guessed. It will even include people that I never suspected. Successful guys that rarely think about that perfectly understandable mistake that happened ever so many years ago will suddenly find themselves wearing orange jumpsuits. They’ll wish they had converted their holdings into Krugerrands or bitcoin, vamoosed to Chad or Yemen, but it will be too late.
Unless they act now.