As far as I know he had no real criminal record. We've heard the same two or three neighborhood anecdotes over and over, but nothing that would suggest he was an obvious murderer. He mostly just seemed like a loser/stoner, and I suspect his mother was aware of that much as far as that went, but I don't think it's reasonable to expect every parent of a severely underachieving teen to have them under 24 hour surveillance/guard. Especially not a single parent with a full time job. 99.9% of teen boys fitting TH's unfortunate outward profile (dropout/stoner/subpar IQ) aren't going to end up killing their neighbor's kids, and parents shouldn't have to behave as though they are.
It's easy to point fingers in retrospect, or to look for another person to blame, or try to think of ways to make it not have happened, but until I have info otherwise it's my gut feeling his Mom had no idea her child was capable of this. I don't think Austin Sigg's mother did either, for that matter. It doesn't mean I think every parent is innocent when it comes to this kind of thing, or that some criminals aren't spawned by their environments. I just think in these two cases, unfortunate single mothers ended up with defective/broken sons.
(It also makes me physically ill to see that people still blame Alanna's parents, in FB comments on the newer articles. It's obvious it's at least partially because of their unorthodox marriage, and they will be hearing this for the rest of their lives.)