Interesting. I read about this a couple of years ago,and I can't remember where I read it,so consider it anecdotal. Here's what I remember from the article:
There was a murder case in the UK somewhere,and since the area was rather thinly populated,and DNA evidence was available(I think skin fragments under fingernails,but like I said this was a while back),the cops took a shotgun approach and just grabbed DNA samples from everyone that lived around there. They got a hit. There was a problem.
The guy that they initially thought did it had been several hundred miles away at the time,and had both witnesses and hotel receipts to prove it.
What had happened was that the cops were using an inital screening process-somewhat of a low cost method-and it only looked for a small number of markers(I want to say eight,but again,don't quote me). The area was fairly remote and hadn't seen any significant population influxes for decades. The same group of families had lived there for quite some time,and what with marrying back and forth,everyone was pretty much related to everyone,and lugging a bunch of the same genetic markers around.
When the cops went to a higher standard test,they found the guy that had done it.
So,I suppose the moral of the story is that,yes,DNA is good,but it might not be quite as foolproof as we like to think. And this story might not have had a happy ending if the initial suspect hadn't had those receipts and witnesses.
Then you conclude that IT IS A PERFECT MATCH, because your JURY doesn't know how many you didn't check. Because 12 of the first 13 matched because they would have matched DAMON,BRENDA, or the boys. The first 5 might have matched everyone in the US.
I am not a DNA testing expert, it would be nice if someone with more knowledge of these procedures could explain what 12 of 13 means. How many markers are there?