The thing is, we don't even know how many deaths there were, if any. They were never mentioned. It is like when the Hulk destroys a city and nobody dies. In fact Captain America says "you have several crimes against you but killing Xavier is probably the most important".
I just checked AvsX and in fact Captain America says "you have several crimes against you but killing Xavier is probably the most important".
Either the lives of people other than Xavier did not matter as much to them or it was material damage. And anyway, even in the worst case, he was full Dark Phoenix. The few moments he was in control he was begging the heroes to kill him so as not to harm anyone else. In all the subsequent status quo they only mention "the murder of Charles Xavier" and "putting the Earth in danger".
Killing Xavier was not Dark Phoenix, it was only full Phoenix, so it was the only thing they had the slightest chance of Scott losing a trial. And yet, as they dive into AvsX Consequencies, Scott probably would have won the trial.
So the United States planned to murder him in prison. This is how they have historically done against the leaders of social movements, not law, just murder.