Of course everyone's first reaction is to lash out and think of something horribly equally to the evil done, but I hope they then slow down and think it through. A guy must be sick to do such a thing, so you've got to get him off the street immediately to protect everyone else. Then think about punishment and rehabilitation, if that's possible.

Indulging in a bloody execution will do more damage to you and the rest of society than it will to the one sicko who needs to be locked up.