Hard question?

Question

Say a man murdered your parents right in front of your own eyes, and made them suffer in the meantime. The man was able to get away. You call the police, but they are unable to find him, and you were the only witness, and you feel that you may not have a case to build against him, because of a perfect strategy he used. A week later you're walking alone at night, and you spot this man in a dark ally. You are armed with a gun. Do you take action into your own hands, and kill this man, risking criminal charges? Or do you leave him be, knowing that he'll definitely kill again soon?

Answer 1

If you don't see anyone who might witness it, then you kill the filth and head home....Tax payer burden solved and justice prevails.

Answer 2

Is the question being posed a moral question or a legal question?  I believe you are morally justified in killing the man, but you are most certainly NOT legally justified.  Your questions also asserts that you "know" he will kill again -- how do you "know" this.  If you had a reasonable enough answer, and the next murder was imminent, AND you had no other way of preventing another murder (like calling the cops), you MAY be able to raise exigency as an affirmative defense.  Your question has enough hypotheticals that it must be a moral question, in which case, probably does not belong in this category.  But, in an attempt to humor you, I've opined on the legal aspect.