"Appropriate" response is wholly determined by what your true goal is concerning the offender. There are four possibilities depending on what you want to achieve:
- Scaring anyone else away from doing the same - well then he must clearly be hanged, quartered and burned at the stake (and his entire family exterminated, including any puppies / kittens / goldfish involved). Apply the same to any neighbours in an arbitrary radius at your discretion, for failing to notice and rat him out sooner. I just hope you don't have a delicate stomach, and didn't plan on using the word "justice" much.
- Punishing him for the consequences of his actions - exactly the same case as above, with the exact same caveat. You're clearly a vindictive bastard and embracing it - you deserve kudos for how well in touch you are with your inner Vlad the Impaler.
- Punishing him for his actions - well now, not to take it lightly but you should think of something seriously inconvenient that will nevertheless be no more than an unpleasant memory and a lesson learned the hard way a year from now.
- (Hopefully) preventing him from doing the same again, by making him understand what he did was wrong, while making every effort not to push him away out of, but to claim him back into society - awww now you gone and done it Sunshine... I got no idea how to go about that, no matter how much I'd prefer this one. Which, incidentally, totally does not mean I think we should stop even trying - but it might take more effort than slavishly applying a set of terse rules whichever way it best serves our sadistic and power-crazed tendencies of glorified apes that we are.