I don't know that the justice system failed. I wasn't a witness, and I haven't reviewed all the evidence the grand jury saw.
IF the justice system failed, heck, even if it didn't and people wrongly think it did, I'm totally fine with them protesting. You can have a million man march for too much mayo on your sandwich if you want, that's fine with me. I just draw the line at busting up property (or heads) of people who had nothing to do with this at all. Burning businesses and looting is NOT taking action against the justice system, failed or not. It's just creating more victims. If people really care about justice, they need to stop turning innocents into victims.