Read through these links on innocence projects, and then move on to the Perfect Evidence show.
Many states have 'innocence projects' which assist in exonerating people who have been wrongfully convicted. The original one is here: http://www.innocenceproject.org/
Their Mission: The Innocence Project is a national litigation and public policy organization dedicated to exonerating wrongfully convicted people through DNA testing and reforming the criminal justice system to prevent future injustice.
Other innocence projects are here: http://www.psychologicalscience.com/psylaw/2012/08/innocence-projects.html
Listen to the show Perfect Evidence from This American Life
http://www.thisamericanlife.org/radio-archives/episode/210/perfect-evidence (below is a summary):
After a decade in which DNA evidence has freed over 100 people nationwide, it's become clear that DNA evidence isn't just proving wrongdoing by criminals, it's proving wrongdoing by police and prosecutors. In this show, we look at what DNA has revealed to us: how police get innocent people to confess to crimes they didn't commit and how they get witnesses to pin crimes on innocent people. There have always been suspicions that these kinds of things take place. With DNA, there's finally irrefutable proof.
What are your thoughts innocence and the sheer numbers of innocent people who may be in prison? What is the difference between actual innocence and plain ol' innocence? Why is DNA so important? What about the cases that have no DNA? What does that mean for people's innocence and ability to prove it?