If the autopsy is to be believed, the police did not cause Gray's death, his injuries were self-inflicted.
Trust me here... If you allowed your kid to ride in the back of your truck without being buckled in and (God forbid) he died as a result, you would be charged with homicide of one variety or another.
Now obviously the charges against the officers are way out of line with the facts. Even if the initial arrest was false (which it wasn't) the facts don't support charging the arresting officers. They helped place the deceased in the vehicle, but he was subsequently removed from the vehicle, had additional restraints placed on him and was put back in the vehicle. How could the arresting officers be held accountable for that? Using the State's Atorney's logic they would be charged with homicide if another inmate at the jail had killed him with a shiv.