The money quote:
For instance, with a 7.5 percent chance of matching at each locus, the chance that any 2 random people would match at all 13 loci is about 1 in 400 trillion. If you choose exactly 9 loci for 2 random people, the chance that they will match all 9 is 1 in 13 billion. Those are the sorts of numbers the F.B.I. tosses around, I think.
So under these same assumptions, how many pairs would we expect to find matching on at least 9 of 13 loci in the Arizona database (65,000 people)? Remarkably, about 100.
And this, ladies and gentlemen is an excellent illustration (better than mine by far) why this idea is so profoundly stupid.