The old saying "two wrongs don't make a right" comes to mind with this.
Lets say that the facts supported the witness and the officer was wrong and shot an innocent man, would that mean protesting violently and looting is acceptable? It does nothing to help your cause, it only hurts your cause.
I just can't wrap my head around the mindset of people that completely ignore facts just because it doesn't support their own beliefs regardless of how distorted those beliefs are.