CPT Nervous
Grandmaster
There's a whole number of reasons why a what from the outside historical view appears clear, isn't to those in the middle.
LEO are often given "advice" by onlookers, e.g. "He didn't do nothing!", "Stop hurting him!", "Let him go!" I gotta imagine that you get to the point where you tune that out.
There's three other officers, so you probably have a crowd influence (forget the name of the bias): Jim is thinking, "Well, Joe isn't concern so I won't be." But at the same time Joe is thinking, "Well Jim hasn't said anything, so it must be all good."
Is there video leading up to this? How did the suspect act? What sort of mindset were the officers in?
That is definitely true. Also, nearly everyone I have had to use force on in recent history has bellowed, "I CAN'T BREATHE" at the top of their lungs for several minutes after they've been detained. I have never held a suspect prone on the ground for longer than it took to get control. People just really like to say that they can't breathe. And you're absolutely right about bystanders, who did not see or know why the suspect is being arrested, but feel like they have to chime in anyway.
Knee on the neck? I don't know about that. I have held my knee on a suspect's back, but not the neck. Sometimes the head if I need to, but again, once they're under control, there's no reason to keep them on the ground like that. If they're compliant enough, we sit or stand them up, and go where we need to go.
I wouldn't call it murder. I'm sure the officer had no intention for Floyd to die. He probably didn't even consider that a possibility. Negligence, sure, but not murder.