There are a lot of videos. I think the guy that initially pepper sprayed him and another protester is the one that also shoots him 4 times in the back. Then I think another couple of shots came from others afterwards.

They shoved a protester to the ground. The guy tries to help them up and is repeatedly pepper sprayed along with the other protester. They then gang on him while he continues to try and help the protester. They then have him on his knees, another one hits him repeatedly in the head with their pepper spray can when the initial guy puts up his pepper spray can and pulls out his gun and shoots him in the back.