This what is called a “lie paradox”.
On the one hand he is claiming that he remembers nothing about events leading up to and including the derailment. On the other, it has been suggested that he may have been hit by a projectile, or at least reported it.
The task at hand is to figure out from statements by him exactly when he “began to forget” about the accident.
“What did you forget, and when did you forget it?”
Wouldn’t you just LOVE to watch them squirm over that one...