There could have been other contributing factors (rock, tough schedule), but it seems likely that their severity will not be known -- the information just is not there.
Surely you would concede that the right course of action here is not obvious?
Sadly, he will not be, because the company needs a scapegoat to cover their lack of adopting the technological safety system that can mitigate the human errors that are inherent in the current system.
If he never drives a train again, every single manager in his chain should be fired--including the CEO as they made the choices to set the system up this way.