I agree on the looting part, but I'd also note that it's unclear that the people protesting the shooting are the same people doing the looting and vandalism. Lumping them all together is exactly what the Breitbart people are doing with such class.
Most likely the protest was started by non-violent people who actually care about the issue at hand, and the rioting was kicked off later by people who don't really give a rat's ass about the cause and just want an excuse to loot and vandalize. That's the way the May Day protests go down here in Seattle, and I don't see any reason the dynamics would be any different in St. Louis.