This guy had few more on top of him, and this “officer” didn’t just press his knee into Floyd’s neck. He on several occasions lifted his boot off the ground meaning his entire weight, or majority at least, was on Floyd’s neck. His body was almost fully erect, meaning he was disbursing even greater force/pressure.
You’ve got mma experience and I have Krav Maga. It is one thing to apply pressure to the neck. What he did was more. He sank great deal of his body (by lifting his boot) into this mans neck. That is fatal over this length of time.
His best option would be to plea for involuntary manslaughter.
Take a gallon jug and see the difference between holding pressure and what happens as you lift your pressing foot of the ground.