That was one of the revelations while I was researching for Chapter 4 of the book, dealing with unavoidable errors in statistical decision making.
The New York Times took up this very important issue in a recent article. Typically, we think that if someone confesses to a crime, the confession is the strongest evidence possible, and guilt is assured. However, criminologists who have studied this issue discover that innocent people do confess to crimes that they did not commit, and not just mentally challenged people. They believe that other evidence will surface to prove their innocence but juries tend to take confession evidence at face value.
The other shocking thing I learned was that it is legal for the police to tell you you failed a lie detector test even if you have passed it. The police also consider lie detector tests as a tactic to extract a confession (because in most courts, lie detector test results themselves are inadmissible.)
The trouble, as the article points out, is that very rarely are such "false positive" errors uncovered and only after extraordinary effort, and therefore the cost to the decision-maker (law enforcers) of this type of error is quite small. That's why the work of non-profit groups like the Innocence Project is absolutely invaluable.
(Thanks to reader Stephen N. for bringing this article to my attention.)