The police claimed that the man was armed and was being reckless with his gun in public, even discharging it earlier in the day. For the first time in a while, for a police shooting that has made national news, the police are able back up their claims with video and eyewitness'. A phone call to the police earlier that day said that this same man was firing his weapon reckless in public, and when the police arrived on the scene he was waving it around with many bystanders near him. Yet, many people still came out today waving their signs and screaming through a megaphone, protesting the incident. Seemingly without even looking at the footage, or the provided evidence. While I can understand anger over recent police shootings, I think you should probably look at the evidence before making your claim.
The L.A. Times provide two different video sources of the incident in their article, here.