This is very weird situation. As I'm working in an animal shelter, I see pit bulls are brought in because they bite their owner or someone before, just like what the article said.
But I don't think they should put the dog down like this, totally disagree what nop said above. I hope they will have a follow up story after the Vets did the DNA test. Imagine that the parents are actually the ones that sexually assaulted the kid and then "created" the scene of pit bull attack/sexual assault, then the parents should deserve to die. In fact, right now the parents (i.e. the pit bull owner) should be responsible as well as they didn't take care their kid probably while knowing they have a canine at home.