He has done nothing wrong, and his captors admit they know he has done nothing wrong. They are doing it just because they think it is fun to watch this innocent person suffer in jail for the rest of his life. It is entertainment for them.
Now...make that person a 17-time murderer, and his captors part of a legal system of a democracy, and preceed the jailing with a fair trial and a conviction, and take away the entertainment that the captors are getting (it is a job now, not fun)...is it torture anymore?