Regardless of the autopsy findings, this is problematic:
It is doesn't take four cops to arrest one man.
The level of force used was not justified by the offence.
When someone in a prone position tells you that they cannot breathe, you cannot fail to respond to this report. Breathing emergencies are life threatening, as anyone with CPR training knows.The officers responded by berating the man, telling him that he can't win.
He went down on his own, the knee on his neck was not necessary to assure custody and control.
There are so many ways that this went wrong that there is just no justification, explanation or defense for it.