Your comment reminded me of an anecdote that apparently, some soldiers in the WWI trenches on both sides intentionally shot to miss. Perhaps when you override that - I'd imagine eventually you do - the amygdala's "firmware" has been altered and one factor of PTSD has possibly been identified.
It makes me think of the initiation/acceptance rituals into certain gangs and crime families where you must kill a man. Then your altered social circuits bond you to other murderers who are your new brothers, and all others outside of the gang are now well and truly the "outsiders". Meaning it's easier to commit greater atrocities for whatever cause driven by a sense of loyalty, tribe and brotherhood.
It would be fascinating if they could get child soldiers from conflicts in Africa in a study like this. One could really get a grasp of what that does to an amygdala when it's not even finished growing. If any person has severe PTSD, it would be a kid who didn't get to grow up "normal".