"He will remain at a secure hospital for life unless doctors deem him no longer a danger."
They've got a long life ahead of them. Surely with actual care they would be released at some point right?
His life is in someone else's hands now, and will be for as long as the government wants. He might be fully reabilitated and regret his actions and they can still write him off as completely nuts with a simple signature in a document - and no one will put the doctor's statement through scrutiny.