The cops fucked up, the question is if they fucked up enough to have contributed enough to a man dying to be legally liable for it.
There was certainly enough for civil liability, but whether there is enough for criminal liability depends on what Chauvin's actual intentions and state of mind were. There are two components of any crime,
mens rea, and
actus reus.
The State has issues with both. The
actus reus prong, that is, the actual act that constitutes a crime, requires proving what Chauvin did actually killed Floyd, and not any of the myriad other issues Floyd had (other than assault because he could have committed some sort of assault but it did not actually cause the death). Or Chauvin could simply have been legally permitted to commit the acts in this case because he was lawfully restraining a suspect, in which case, even if it caused Floyd's death, he still isn't guilty.
But even with
actus reus, you still need
mens rea, a criminal state of mind. This has to be more than simple negligence, and it varies for the different degrees of homicide charged here. The only place where
mens rea is fairly easily provable is in some form of assault. Chauvin clearly intended to commit the physical actions he did. For anything else, he has to have either actually intended the result, that is, the death of Floyd, or show reckless disregard or depraved indifference as to the result.
Depravity is a fairly high bar to clear. One of my favorite quotes about it is it requires an "abandoned and malignant heart." That's one of those phrases that sticks with you.
Incidentally, this is why they're really laying this on thick. They want the jury to believe Chauvin is a depraved demon, a monster, who would be capable of such an act. Chauvin just being an imperfect man who fucked up doesn't cut the mustard.