"I went for a very rare trip to the cinema last and watched the Sweeney. I know its not entirely factual but I'm sure a lot of police officers were probably like that back then, ie hanging suspects upside down off roofs until they got answers. Of course that doesn't happen now but you have to sort of think well they had a point, if it got the answers."
The problem was it so often got the wrong answers: people confessed to things they hadn't done and couldn't possibly have done just to get out of there, meaning that investigations went down the wrong track and the real perpetrators got away.
Think about it, if you were in pain, not allowed to sleep for days on end, humiliated and frigthtened, which would you rather tell- the truth or whatever you thought most likely to make the whole thing stop?
There are good reasons why torture is not allowed - and it's not all about consideration for potential perpetrators, either.