He didn't have a gun when he was shot, what are you talking about? He didn't even have a gun in his hand. Or you mean that you can accidentally shoot somebody who had a gun, at some point in the past?
I think you can shoot someone if you have reason to believe that somebody has a gun. In this particular occasion the guy did not have another gun.
(Hence I'm calling it an accident, where the police officer may be at fault. Though, other commentators saying it was cold blooded, a death sentence, deliberate, etc. is not true. Nor is generalizing this particular situation to changes in government type. These people really want to portray their political opponent as bad as they possibly can.)
You should not carry a gun to a protest, not engage physically with an officer nor resist when they start arresting you after that.
You should watch the video. While seem to be an accident, a way to avoid it would have just been not bring a gun in the first place nor engage physically with law enforcement.
These actions in general to restrict law enforcement to do their job isn't helping either. Protest in front of government buildings, not follow police around.
You should watch the video, the police are the ones who engaged physically: pushed Pretti, pepper sprayed him, dragged him on to the street, hit him on the head repeatedly, and then got scared and shot. You can protest wherever you like that's legal. If police cannot handle that (start fights and then get scared and shoot) they shouldn't be police.
Also, it is absolutely legal to follow police around. It doesn't make sense to make something legal while justifying getting shot for it (unless you want to make it illegal eventually).
No, they started the engagement. What's wrong with trying to help somebody pushed to the street? Or are you recommending just letting police push people with cell phones to the ground and pepper spray them, unless you want to be shot dead?