The length of time that the officer had his knee on Floyd’s neck, those around him telling him that he’s killing this guy, he had to consider what he was doing and the prosecution may very well have a case that due to the extended time, at some point, it became premeditation because he chose to continue in spite of all the evidence that he should now stop.
I don’t think it has to be prior to the altercation, but rather prior to the act. For example, they’ve got him cuffed and sitting on the curb. He tells one of the other cops “I’m going to kill this guy” and the state can prove it. He walks over, gets him down and puts the knee to him.
There is a possibility Derek Chauvin and George Floyd were aquatinted before their fatal encounter. It’s not known if they interacted, but it’s possible the two weren’t strangers, making Floyd’s death something other than white police officer vs unknown black subject.
I would think it possible, then, if premeditation could be proved, this would up the ante from manslaughter to first degree murder.