I wish I had the actual news story to show you. The point was, he believed exactly what you do. But it wasn't true.
He thought that he could confess, retract the confession, and they couldn't convict him without some other evidence, because he wasn't really guilty.
He believed false convictions in a murder case just couldn't happen in this country.
However, as the New Yorker article said http://www.newyorker.com/magaz... when a jury has a confession, they always believe it. Even if the suspect retracts it, even he was manipulated into confessing, even if the police lied, and even if there's independent evidence that he's innocent.