Every rapist, murderer, thief, etc must have swallowed hard upon hearing how the cops got the Cali serial killer
On average in the US a person has about 300 3rd cousins, about 100 2nd cousins & anywhere from a handful of 1st cousins to over 50 depending on family size. Personally I have over 1000 DNA relatives already in the 23 & Me system.
No one knows all these "family members" & certainly can't prevent them from submitting their DNA. That means that as soon as cops can ID a relative they can narrow down the field of suspects from nearly anyone in the country to, in many cases, under a hundred people or less if the relative was a close match like a first cousin, aunt/uncle, sibling, parent, grandparent or kid.
Since DNA already identifies the gender of the perpetrator the pool of possible suspects is cut in half right away. Combine that info with the location the crime/crimes were committed, cross that with your list & you've significantly focused the investigation to what might be just a few people if not ONE.
If any other details are known about the perp like hair color or even what brand of tire left impressions at a crime scene that also narrows the possibilities.
Once cops narrow the pool, those people will be followed around for a flicked cigarette or discarded cup to see if they've "got their man". This is a major leap forward for crime solving & should have freaked out everyone who committed a crime that cops have yet to solve.
I gave 23 & Me a whirl years ago before the sinister potential of such services was considered. If one of my relatives turned out to be a killer or rapist I would have no problem allowing the site to reveal my identity so that a family tree can be built to ferret out the criminal. I suspect most people would not take issue with that. Furthermore, cops may only need a warrant to get my identity or yours anyway.
Unless a person is a first generation immigrant here they probably already have a myriad of relatives in DNA banks. The more "hits" (DNA relatives) the cops get, the easier the killer/rapist/etc will be narrowed down.
Every unsolved case where DNA was collected now has a MARKEDLY INCREASED chance of being solved. Criminals everywhere should be on notice
One of these days your DNA is gonna get you
Frankly, rapists should just hang up their hats & wait for the police. Even with a condom…it's very hard to rape someone and not leave a trace of genetic material. CONSIDER THIS A WARNING.
COMMIT A CRIME … EXPECT TO DO THE TIME