I don't know where I read it, but it's all based on a school of interrogation that is totally dodgy but court approved and because it gets results (ie convictions regardless of whether they're right or wrong), Police departments aren't going to stop using it.
This is the one: http://www.newyorker.com/magazine/2013/12/09/the-interview-7
It's a long read, but really fascinating. I might have gotten the link from someone in this thread actually, so credit to them if I did!