Four men are seeking certificates of innocence after prosecutors dropped rape and murder charges against them last week. They each spent more than 15 years in prison and the cases come on top of another five men who were recently released for a 1991 murder, which makes nine people in the last few months in Cook County alone.  Cook County State’s Attorney Anita Alvarez  joined Eight Forty-Eight to discuss how her office has been revisiting these difficult cases. WBEZ criminal and legal affairs reporter Robert Wildeboer has been covering these cases and joined the conversation with some additional background.