and what do you want the cop to do ? he had a gun and wouldn't drop it, maybe he could hold court in a pitch black alley to find out if he is the baddy , take statements from those screaming emotional probably drunk idiots, while the guy has a gun and has already shot someone and who knows who else is involved and also armed, even the woman on the phone couldn't string a sentence togetherWe don't have the full context here.
It is possible more than one thing happened here and the guy on the ground is not the bad guy, possibly.
But Cops just shoot everyone so no surprise they kill him.

