There’s no indication that they knew each other when they worked security for the nightclub/bar. There was an inside security group that Floyd was part of, and a parking lot security group that Chauvin was part of. It was the bar manager or owner who realized that both had worked there.
It’s clear from looking at the video that Chauvin was greatly enjoying his power to inflict pain.
A psychiatrist would proffer that Chauvin is a Sadist. When he digs his full weight into Floyd’s neck, you can see Chauvin place his hands into his pants, close to his crotch. He seems to be pleasuring himself, as he looks down the defenseless victim.
Is this why Chauvin refused to remove the knee from the victims neck? He was trying to attain a sadistic orgasm?
If this ever goes to a jury trial, the prosecutor is going to have a field day with this case.