As a cat owner, all I can say is if a cat has a collar there's (as far as I know) no law against them being outdoors, assuming all their shots are up to
date. I had an outdoor cat before, and there is no way in hell I could stop him from climbing up trees, jumping on people's decks, sleeping on their
cars... unfortunately there's no way to control a cat when it's outside. I understand your frustration and I'm sorry, cuz I know I'd be pissed
if it were reversed, but unless the owners stop the cats from going out (which, once they've already been out is quite hard to do), I doubt there's
much that can be done 
