You seem to not get it. If he want for the gun and the cop shoots him, good. Blacks are not saying they want criminals to get away, they are saying they want equally treatment by the law which has historically profiled, harassed, abused their power when it comes to blacks. Unlike whites who view the justice system as fair this is not the case for blacks, because historically the justice system has not been fair to blacks. Consider that in many states even in the early 1900s, blacks could not testify against whites, if they weren't property owners.
The biggest issue here is you see the law as lacking bias, so you figure a just result is the norm, this is not the case with blacks. I brought up OJ because it's the one time whites got a taste of how blacks have had to deal with the law for centuries.