You know, perception is reality. I watched the entire 33 min video. There are two very interesting parts. First the 10 -15 minutes before the violence (Things I noticed: He told the cops his name, they didn't seem to buy it or just wanted to hassle him over it - not sure. Kelly let them search his backpack. Kelly followed directions, but had to be told repeatedly, its unclear if he always understood what he was supposed to do, but an effort to comply happened throughout. Interestingly the verbal threat from the cop came somewhat out of the blue and up to that point Kelly had complied with all orders despite confusion/inability to remain at attention or on task. (Duh, he had mental problems)
The second thing that is interesting happens while the cops sit on him. They sit on him and speculate about Kelly resisting once they let him up. A second before they get off him and realize he's not breathing, one of the cops says "He's going to fight." So the cops had a belief he was going to fight, even as they sat on a now unbreathing (dead) Kelly. They get up and seem a bit surprised that hes not breathing. Then the excuses start :"he must have been on something" and "I ran out of options" You don't have to be a psychologist to recognize their attempt to justify and distance themselves from the results of their actions. So perception is key here: They perceived him as "fighting" even when he was dead/unconscious.