Is this how our system works?

The press persists in calling the lawless rioters/looters/arsonists/thieves in Ferguson, Missouri, demonstrators. They say that the demonstrators are demanding justice for Michael Brown. From what I've seen and read, Michael Brown received justice about two weeks ago.

At any rate, their definition of justice is "Ferguson police Officer Darren Wilson is charged and convicted for the shooting." I don't think that's how our system works. In the first place, we don't know that Officer Wilson is guilty of any crime. The evidence may show that he was justified in what he did. In the second place, it's up to a jury, not a mob, to decide whether justice entails a conviction.

If they're so concerned about justice, what about justice for Officer Wilson? What if Officer Wilson is guilty of nothing but defending himself? Is justice served if he is convicted of a non-existent crime? Let's reverse the races. What if Officer Wilson were black and Michael Brown were white? What would their definition of justice be then?