And yes, I understand that he is devastated by the death of his own child, but that is a terrible, terrible (non)reason to extend abuse towards other people's children.

I'm sure he is in a lot of pain and needs a grief counselor to deal with his own child's death; however, I'm not convinced that losing ones child automatically turns one into a child abuser, and my deep suspicion is that he likely committed abuses toward his biological children as well. I get that he blames the mom, but again, I don't see the psychological profile indicating that the loss of a child, even at the hands of another adult (in his mind) statistically results in one suddenly beginning to abuse other children.

My guess is that like any abuser, he was abused as a child and has simply, sadly, become like his own father and/or mother or whoever hurt him.