People thinking how complicated this must be to filter through for forensics, forget that during and following the Covid lockdown, cities monitored sewage water for Covid viral load. They even recognized and reported the specific strains and their dominance in the samples. This includes finding "new" strains, and all this among all the other DNA/RNA bits to be found in city sewage.

So the technology is indeed there to find the needle they're after in the haystack they're provided.