That is just awful. The only theory I have is that there are people out there who are without a conscience or a soul and allow evil to consume them. A lot of people cry "insanity" in the courts when things like this happen, but I think that is way overused.
I've never understood how anyone could kill a helpless, innocent little child -- there are too many of us in the world who would gladly take them, love them and raise them as our own. When I hear of things like this, I sometimes blame the child welfare/protective system. I can't help but wonder if they pushed some of these creeps to sign away their parental rights and get the kids out of those environments like that and streamlined the domestic adoption process to eliminate a lot of the governmental gobbledygook; if at least in some cases a child's life could be saved. Even if it was just one child, it would be worth it. However, the pencil pushers that work for CPS have the philosophy that it is better for children to stay with their biological parents -- doesn't matter that they may be an axe murderer. Such a tragedy. =(