I remember watching a documentary once about people who do this sort of thing. Nine times out of ten they go on to do the same thing to human beings. I think Jamie Bulger's killers may have been mentioned.
But what does the law do when they're caught and convicted for animal cruelty? Gives them a fine, a cso and oh, wonder of wonder, a ban on keeping animals! Like that's going to stop them! Perhaps if such crimes were taken a little more seriously then those who commit them wouldn't get to reach the higher levels of depravity that makes them kill equally innocent children.