I feel like these situations make the implicit assumption that violence is the ONLY possible way when it is in fact just the easiest and fastest way, with very mixed and inconsistent results. In the given situation wouldn't the obvious thing be to offer him total immunity? Was making sure he was punished for something worth the life of the child? What if he had given them incorrect info just to make the beating stop?

I would say yes they were in the wrong. It was a bad choice even if its one I would likely make myself. Maybe the insistence that morality is strictly on a continuum from "good" to "bad" is part of the issue.