I don't like the phrase "unlawfully killed". Call a spade a spade, he was murdered, or if we think the state was culpable, executed without trial. I don't think shooting a man with a knife is a proportional or defensible response either, honestly. I can see why police would want to restrain or arrest such a man, but the fault is with the police entirely if they then choose to kill someone. If you're running around pointing a live firearm at people, wearing full body armour, you have no business feeling excessively threatened by someone who is only armed with a knife and certainly no business killing them.
I agree that the militarised police are a major part of the picture. I think a very disaffected, poor, unemployed underclass in the form of Ferguson's young black community seems to also be a problem - it's not just the response that's the issue, it's massively higher sentencing rates for blacks and continued racial profiling policies and anger at that is boiling over. Burning and looting clearly needs to be addressed at some stage, but right now the police need to stand down and de-escalate the situation, confrontation is only increasing the levels of property damage.
Also apparently Egypt has called on the US to show restraint in dealing with protestors. Which I think may be the final straw to show just how badly this is going.