The guy was treated and released by the hospital, then immediately taken to police headquarters. Black boxes have been recovered. One must assume his phone records have been reviewed. Officials already know exactly what happens here.
My personal opinion is his mass suicide attempt failed. Now he’s in deep kimchi. He will be very popular for the rest of his life behind bars.
then immediately taken to police headquarters.
He did apply full emergency braking just before the derailment.
My guess is that he was paying attention to something other than driving the train.