My own personal take is that it is quite possible that Chauvin did not really need to keep his knee on Floyd's neck for 9 minutes. They had him handcuffed behind his back, so they could have tied his legs together and thrown him in the police car or a van.
However, according to the autopsy and the testimony of the doctor who did the autopsy, there were no injuries to his neck and his death was not caused by asphyxiation. So how can anybody say that the police officer caused his death?
Furthermore, they charged him with manslaughter, 3rd degree murder, and 2nd degree murder. I am not a legal expert, but how can they charge him with all 3? I think they should have been required to pick one and prosecute that one - this has made a farce of the legal process.