In the 1963 case of Brady v. Maryland, the U.S. Supreme Court ruled the Constitution requires prosecutors to hand over to the defense any evidence that tends to prove the defendant's innocence. When they do not and the defendant is convicted, their failure or refusal to do so can result in a new trial.
The National Registry of Exonerations has just released data on the 139 people known to have been exonerated in 2017, along with historical data. This information gives us some insight into why 139 innocent people ended up behind bars, and how they ended up getting freed.
When a defendant is exonerated, what happens next? Suppose the defense proves that DNA evidence from the crime scene does not match the defendant. Or, perhaps a key witness recants their story. In some cases, misconduct by the police, prosecutors or the jury is discovered. Once it's clear that the prosecution's case is insufficient to prove guilt beyond a reasonable doubt, does the defendant walk free?
When Wilbert Jones was convicted of a 1971 abduction and rape, he was 19. He was sentenced to life in prison without the possibility of parole. Now 65, he is tasting freedom once more after a Louisiana judge ruled the case against him was weak and found that prosecutors may have withheld key defense evidence.
Halfway into a 20-year sentence for murder, Jennifer Del Prete was released on bond in 2014 after a judge found she had demonstrated her "actual innocence" of the crime she was convicted of. She had been convicted of violently shaking a child in her care at a day care center. That alleged shaking caused so-called "shaken baby syndrome," neurological evidence of abuse. Unfortunately, it appears that the science behind "shaken baby syndrome" is, as the judge put it, "highly suspect."
A man who has been serving time since 1995 for the murder of a drug dealer has been released with his conviction overturned by a judge. That judge found evidence of serious prosecutorial misconduct that made his trial and conviction unfair. The district attorney's office is appealing the decision.