If the circumstances are that he attacked a police officer who was clearly identified as such, after merely being questioned and/or confronted by said officer, and if that attack involved hitting the officer in the face and attempting to gain control of his firearm...
Then I don't even consider "murder" to be a possibility under that set of facts when we're talking about a window of time from start of encounter to Brown shot dead which is a matter of just a couple of minutes, tops.
Something pretty outlandish would need to have happened for me to think "okay now THAT is murder" like Brown on his knees, hands clasped, begging for his life and clearly not a threat... and Wilson clearly seeing that and still opening fire anyway, past any heat of the moment zone.
But this isn't that. This all happened very fast and Brown was doing things contrary to Wilson's commands very close to the time he died. Within moments of it. When we're talking about an injured officer facing two people, and opening fire mere moments after sustaining that attack... well, I'm just not inclined to judge his actions too harshly.
And remember there are legal provisions for a cop killing a fleeing violent felon so I'm not in crazy land here.
It's a hectic life and death situation the deceased created. Would take a LOT for me to feel the cop had done something worthy of prosecution.