The kid did good in getting involved but the above quoted line is why he never should have let the guy walk away. When someone is as deviate and violent as this perp he should be prevented from leaving the scene by what ever means necessary (although when you think of it what good does it do to nail the guy? They'll just let him out.)
The kid did fine. These things are rarely clear. e.i. Is it a husband and wife, a bad drug deal, or an attempted rape? I interjected myself once on a situation where a woman was getting beaten up. I stopped a very bad scene, and I'm glad I did, but vice being abducted she was being beaten for not paying for her drugs. Had I capped the guy, I likely would have done jail time. Still, much better than turning a blind eye. You just have to be careful.