I agree murder is not supported by the evidence. The best possibility might be involuntary manslaughter, however even that is shaky. I suspect there will be no criminal charges unless MN has a statute that covers the failure to render aid. Any one of those officers could have exercised the common sense to check vitals once Floyd was unresponsive. It is likely this failure to act is what got them fired. Their indifference toward the well-being of Floyd is appalling, when even the bystanders are pleading with them to do that one simple task that is within their training and could have saved him.
My own summation based on the audio and video-
Floyd was compliant initially during the encounter and was handcuffed before officers even arrived. Officers determined to arrest him either for the counterfeit money or for being under the influence of drugs. They escorted him across the street to their vehicles where he resisted when they attempted to put him in the back of the vehicle, apparently complaining about a bad knee. This resistance resulted with Floyd facedown beside the vehicle with all three officers holding him down. It isn't clear how aggressive Floyd may have been, but the allegation that he was under the influence coupled with the officer's reactions suggests to me they had significant difficulty with him. Handcuffs restrain, but they do not prevent combative behavior.
Rather than continue to fight with him over getting into the vehicle the officers opted to hold him in place and await the arrival of the ambulance.
During this time Floyd became obviously unresponsive and all four officers failed to do anything at all to at least check for a pulse or show any interest whether he was alive.
None of that leads to a murder charge, even with the officer's knee on his neck. Personally I suspect the weight of other officers compressing the chest was a bigger problem, or the stress coupled with drugs may have even caused a cardiac arrest. Cause of death won't matter. No matter what the officers failed to act when they had opportunity.
The PD policy and procedure manual, available on their website, specifically indicates the neck restraint as an allowable NON-DEADLY force option. It is unknown how much pressure was even exerted on the neck as Floyd was able to talk initially, and the officer does not appear to be exerting himself. I think the only intention was to restrain, not to choke, restrict blood flow, or to kill.
This piece of policy that ok's what the officer did is why he is unlikely to face any criminal charge for manslaughter. He received training in a non-deadly technique that resulted in death, but was the death from the technique or something else? Doesn't really matter because the technique was allowed. The officers encountered resistance and an authorized non-deadly option was applied.
The death was accidental. Nobody intended to kill Floyd. There will likely be a civil wrongful death payout because the officers failed to exercise due care, but criminal action just doesn't seem likely.
I'm not sure what the federal investigation might make of it. They would likely try to call it excessive force if anything, but we go right back to the officers using a trained non-deadly option within department policy. They didn't know he was going to die, and it is unreasonable to expect they would all go along with it if they did.