Why isn’t Andy sent to a psychiatric institution?

Law enforcement, the courts, and the federal agencies in his area know full well what a criminally malicious threat he is. I don’t believe he’s normal in the head, he does have a legitimate mental illness and he has time and time again demonstrated what a menace he is to society and the potential threat he poses. So why isn’t he institutionalized? What exactly does Andy have to do criminally to get locked up in a hospital?