I read that story and it truly is disgusting. I can’t think of a punishment harsh enough to deal with that guy, but I can tell you, I would do everything to make the perpetrator’s remaining days on Earth a living Hell.
Think of those children whose lives he has destroyed. Personally, people like Fritzl show why we need to reinstate punishment such as crucifixion, the brazen bull, ritual dismemberment and torture. Partially, it is to give the man as torturous a send-out as humanly possible, but also to serve as a warning to any other perverts who would seek to copy this man’s heinous actions.
Barring that sort of execution, put him in the general population of the prison and let the guards take a walk for a couple hours. I don’t think there can be any sympathy for this guy’s actions.