Floyd was an ex-con who resisted arrest. Once he resisted arrest he bore responsibility for what subsequently occurred to him by the police.
That said, it seems at first glance that the officer who pinned him down acted excessively. If so, that officer also bears some responsibility. Nevertheless, the officer had both the right and obligation to subdue Floyd, who was wrongly resisting.
So the question becomes how to break down responsibility for the terribly unfortunate result between Floyd and the officer holding him.
The other three officers bear absolutely no responsibility for what occurred. One of them, in fact, asked the officer pinning him to ease up. None of the three others ranked above the officer holding Floyd that they could have ordered him to let up.