The Innocence Project provides several reasons why people are wrongfully convicted, including eyewitness misidentification, false confessions, police misconduct, prosecutorial misconduct, improper forensic science and jailhouse informants.  Reforms in these areas will lead to fewer people being wrongfully convicted, but it is not going to help the innocent people sitting in prison as you read this.

In case you're wondering, 10 wrongfully convicted people in Pennsylvania have been exonerated and released from prison.  This does not sound too bad, unless you're the person who has been sitting in prison for 20 or 30 years for something that you did not do.