Though it's hard to say for certain, waddn there at the time to know what really happened and why. But .... from the sound of things the cop over reacted and killed someone without any seemingly valid reason for having done so.

This shit happens, though it shouldn't, it does. Humans are basically flawed beings, some more than others, but normal people, cops and every one else fucks up. Sometimes people even die because of it. Wish it waddn so, but that ain't about to make anything better and it damned sure ain't gonna change basic human behavior.

All that said, if anyone, cops included, fucks up and someone dies because of it, they should all be held to the same level of accountability, period