They could only charge him for murder, manslaughter or involuntary manslaughter. The prosecutor would need to prove that Chauvin left the police station with the intention to kill Floyd to charge him with murder. This would most assuredly not lead to a guilty verdict. The U.S. seems unique in that you can be charged for all three at once at varying degrees of severity per charge. In most European countries it would 'just' be manslaughterThat seems worse, actually; if they get off the stronger charge, but would've been found guilty on a lesser charge, then the defendant gets off even if the jury believes beyond reasonable doubt that they did it.