From what information we have, the father is justified, not in intentionally killing the criminal, but in beating him up and killing him on accident which is probably what happened.
But people shouldn't be so quick to accept a story.
How do we know for sure he was a molester? Is it out of the question that the father could have come home drunk, misunderstood the situation and killed an innocent man? Just saying people shouldn't be so quick to turn this man into a hero.
Also, even if the story is legit, he killed a man with his bare hands in front of his daughter. I don't think that's very considerate.