So it depends on what Derek Chauvin was thinking. If he walked into the situation thinking “I’m going to kill that guy”, it’s first degree. If in the moment he realizes “I’m killing this guy” and continues, that’s second degree. If he just thinks “Eh, if he dies he dies”, that’s third degree. If he should have known that Floyd’s life was at risk, it’s manslaughter even if he didn’t know.
In my personal opinion, the Floyd killing is second-degree murder. But if I wanted to give myself the best chance to win in court, I’d do what the prosecutor has done. I’m not sure I could prove to a jury that the thought “I’m killing this guy” went through Derek Chauvin mind (though being surrounded by people yelling “You’re killing him” should have given him a clue). Proving that Chauvin acted recklessly and should have known Floyd might die seems much easier.
I don’t want to hear the platitude that violence never changes anything. In fact it does, and I think we’re seeing that now. The riots are sending white America the message that this can’t go on. It could have heard that message when Eric Garner said, “I can’t breathe.” It could have understood that message when football players knelt. But it refused. Now the message is being sent with fire and broken glass.
So far, a lot more is being said about these mystery men than anyone actually knows. Some say they’re white supremacists trying to set off the race war that their rhetoric says is coming. Trump says Antifa is behind it.  A number of protesters in Minneapolis suspect undercover police of agitating the violence to discredit the peaceful protests. (In the Umbrella Man video, bystanders keep asking “Are you a cop?”)
Any of those stories might have been false originally, and then become true. If you’re an isolated white supremacist or a left-wing anarchist, and you hear a false report that people like you are trying to turn the protests into riots, maybe you go out and do it without orders from anyone.
My advice: Pay attention to actual cases and the observations of specific witnesses, but don’t take anybody’s conclusions seriously yet.