As far as protecting innocents, absolutely. But it cannot done in a manner that penalizes the person in a manner unauthorized by the Torah.
Incorrect. The Halacha is explicit not like you. The Shulchan Aruch, Rema, Sma, and Shach all say in the second siman of Choshen Mishpat that if there is a real problem in a community with a certain issue, the ones in charge are authorized to take measures not sanctioned by normative rules of Choshen Mishpat – even if that means killing the person, or any other of penalty (as long as we are authorized by the government to do so of course).
A deterrent is needed. There’s no better way to say it – it’s simply tough luck on this kid.