Why would an innocent person confess to a crime he didn’t commit? The answer to that question is complicated and a bit counter-intuitive, but there is an answer. Here are two great links to help you wrap your mind around the problem.
First, This American Life, episode 507: Confessions, from October, 2013.
Next, a Fresh Air interview by Terry Gross of Douglas Starr, Beyond Good Cop / Bad Cop, which aired on December 5, 2013. Douglas Starr’s article, The Interview: Interrogation Techniques and False Confessions, is available in the December 9 edition of The New Yorker.
The links and the article might not tell you everything there is to know about false confessions and their relationship to wrongful convictions, but it’s a damn good start.