It happens very often. I have friends who are defense lawyers. They get very frustrated at the how the system fails. We also had 3 major crime lab scandals h

It happens very often. I have friends who are defense lawyers. They get very frustrated at the how the system fails. We also had 3 major crime lab scandals here in Massachusetts recently, all of which revealed that thousands of folks were put away with bogus evidence. See also The Innocence Project, who are constantly proving that people on death row were in fact innocent.