"What's wrong with him? Is he nuts?"
What tipped you off, Mr Detective? The fact he sabotaged someone's expensive car, broke into her apartment, and stole her pet for blackmailing purposes, all for an extremely bizarre reason? Not to mention he'd have hit Saotome when speeding out of the car park, if Shun had not been there to save her. Was that the hint? You don't need to be a psychiatrist to recognise a schizo based on such ample evidence.