If he has an episode, there must be a sign.
Because there has been no mention of medical record, this leaves the question to look back at his background more clearly.
In this situation, the most important thing is to look for evidence or witnesses. But he himself had found out there had been no change in reaction to his odd behavior. Based on those assumption, it is possible that the testimony of his girlfriend or the people around him is wrong.
Also, about the timeline : what he did, where did he go, etc.
During the investigation, it will be very interesting if he finds something contradictory, which makes him increasingly cornered.