It all comes down to this though. Would you do the same in the cops situation? I would. The guy was a known gang banger with a history of violence, in fact he committed an act of violence the very same day. He would not listen to the cops commands and instead it appeared he was reaching back into the truck for something (they were told by his wife he had a throwing knife), and the cop has to assume it is a weapon of any kind. We know now it was only to untangle his leg, but the cop did not know that.
When in a highly charged situation like that, one blink of an eye of hesitation on the cops part could very well mean the loss of their own life.