A policeman also needs to do snap judgments sometimes and may be tired.
Nevertheless, we expect him not to kill without a reason that withstands a judge's curiosity - or else he faces and deserves serious problems.

Extenuating circumstances aren't the same as "not guilty".
Also keep in mind that these men were highly trained and not mere enlisted personnel or even conscripts. You should be able to have high expectations of their judgmental abilities or else you shouldn't entrust them a multi-million dollar machine of war for a combat mission over a densely populated city.