That was murder. Kneeling on the man’s neck for minutes after he becomes unresponsive, after he loses control of his bladder.
Murder.
It’s at least manslaughter. Police have a very difficult job, but there is no excuse for suffocating someone to death with your knee on their neck.
While the cop deserve jail time, I don’t see this as murder. I think it qualifies as manslaughter, particularly involuntariy manslaughter. Murder involves an intent to kill someone, either with premeditation or rashly on the spur of the moment, or being instrumentally involved with someone else doing so.
Killing someone out of careless negligence is almost always manslaughter, but I share your outrage at what the cop did. He needs prison time and to lose his job forever as a felon.