people say 'how do we know what was going on in the cops head' and 'maybe he really did fear for his life'.
Cops should NOT be human when it comes to issuing bullets. They should be well-trained machines. They have unlimited officers (call them on the radio), they have lethal and non-lethal weapons. They're well trained in the use of both. And they've had plenty of classes on THE LAW and when they can/cannot shoot. In this situation, they also have the advantage of being standing and not handcuffed, lol, which the dude on the ground sure didn't have. They are trained so this DOESNT happen, so we don't have to worry about the individual fragile mindset of individual officers. Their reaction should always be... the LAW.
This could be any of us. Let's say we're at the bar, enjoying a drink, and our shit gets spiked, we have a reaction, and suddenly we're bouncing all over the place in handcuffs, out of our head, angry and scared, whatever. Cops handcuff our ass. We don't know why the dude fought - mental illness, drugs, or just being a jerk. Cops can add more charges for resisting - they get their justice when he gets another month added to his sentence for their inconvenience that day. But they can't just shoot.