I don’t remember the exact details, because I have watched it long time ago, but they don’t need an exact match. Actually it’s more scary - if your distant cousin has DNA “in the system” - you are in it too.
This 1M DNAs may “help” match an order of magnitude more people.
I think you're thinking of genetic genealogy, where some of those DNA testing providers (like 23andme) submit their records to law enforcement, and they can see something like "this DNA sample is likely to be a brother of this existing sample", and can narrow down investigations based on that
I don’t remember the exact details, because I have watched it long time ago, but they don’t need an exact match. Actually it’s more scary - if your distant cousin has DNA “in the system” - you are in it too.
This 1M DNAs may “help” match an order of magnitude more people.