This is i feel. In the midst of a war, you might be in a situation where killing someone is the best/only means of neutralizing a foe that is putting your life / your comrades lives in danger. If another way to neutralize them were available, it would almost always be preferable (For many reasons, not the least of which being the great mental toll that taking another life has, resulting in often life-long conditions similar to PTSD called Perpetrator Induced Stress Disorder), but like I said often that's not the case.

Outside of a wartime scenario though, there should be a plethora a options available to neutralize such a threat. In fact, going all the way to jump right to killing them almost imbues them with a seemingly inhuman power. My feelings on 'justice' is that first the threat should be neutralized, second is restoration: righting all the wrongs as much as possible, and third would be the transformation of the transgressor to acknowledge and move past their antisocial behavior which often can open eyes of would-be transgressors perhaps even in a cascading effect. If they're killed in the first step, it can make the second step much harder, and the third step impossible.

And I really think much more attention to should be given PITS. someone needs to do those killings, if there is someone who is to be executed, and the effect it'll have on the executor can't be ignored.