On Thursday morning, two armed terrorists, murderers by definition, were shot and neutralized by soldiers from the Israel Defense Forces Kfir Brigade, which efficiently prevented them from carrying out their deadly plans. The terrorists were now lying on the ground, incapacitated. IDF soldiers had thwarted the possible murder of innocent Jews in the Tel Rumeida neighborhood of Hebron, a place of constant friction between Jews and Palestinians. They did the right thing. However, a few minutes later, one of the soldiers shot one of the terrorists in the head. Not only did this horrible act shock the small crowd of already inflamed Jews and Arabs nearby, it also sent shockwaves through the government and defense establishment -- as it well should have. The time that elapsed between the moment the terrorists were neutralized and the moment one of them was shot in the head after having already been subdued should be the focal point of the investigation into the soldier's actions. The situation is quite clear cut: Knife-wielding terrorists with the clear intention of killing Jews anywhere between the sea and the Jordan River are deserving of death and must be shot without hesitation. Perhaps Defense Minister Moshe Ya'alon and IDF Chief of Staff Gadi Eizenkot should reiterate that. Nonetheless, there are three scenarios in which we must hold our fire: When the terrorist drops his weapon and/or puts his hands up in surrender and/or is neutralized on the ground. The incident Thursday morning in Tel Rumeida fell under one of these three exceptions. Eizenkot's directive to leave no stone unturned in investigating this event is a step in the right direction. It is likely that the shooter will argue that the terrorist still posed an imminent threat to his life and that he suspected that the latter was wearing a suicide vest. Alternately, the soldier could also make the mitigating claim that he was under emotional turmoil and scared to death to the point of losing his composure, which will not exonerate or exempt the soldier from punishment, but could very well reduce his sentence. IDF Spokesman Brig. Gen. Moti Almoz, who accurately explained the effect of difficult dilemmas on the IDF's combat ethics, wisely avoided addressing the many calls made by politicians and rabbis to kill terrorists. Indeed, the government's role is to instill in the fighters, and consequently in the Israeli public and in international public opinion, the fact that the IDF's military conduct is a two-stage operation -- soldiers are free to open fire at full force to counter a terror attack, to the point of neutralizing the threat. There is no compromise on that. If the terrorists are killed in the process, there is no wrongdoing, despite the extreme Left's outcry, be it in Hebrew or Arabic. But once the terrorists are incapacitated, that is where the line must be drawn. Even if the terrorists are not hurt at all, the shooting must stop at that point. This is the true meaning of the IDF's "purity of arms," a term which our enemies seek to rob from Israel's vocabulary and history.