All human life is sacred. At the killing of Abel by Cain, God decreed that killing a human being is like killing all mankind and saving a human being is like saving all mankind.
Only in cases of war is it permitted to kill a person who is of the military of the enemy, but not of a civilian. Life may be taken in the course of justice as punishment for murder, treason, and rebellion.
It is forbidden to kill a non-combatant even in the heat of battle on a battlefield. Compare this with what nations at war do today, calling it mere "collateral damage", the killing of innocents, including women and children, by the use of bombs and missiles that do not discriminate. In World War II, both sides freely targeted civilians, women and children, in the fire bombing of Dresden, in the V2 attacks on Germany, in the use of atomic bombs on Hiroshima and Nagasaki. The mindset that babies can be blown to bits deliberately to win a war is barbaric, yet so-called "civilized" nations are unashamed and unapologetic, and continue to target civilians and use bombs and missiles in civilian areas, knowing that many innocents will be killed. Muslims who deliberately target innocent persons are no less guilty of a criminal act than non-Muslims who do so.