Almost all of them occurred in Illinois, where 13 El Rukn gang members received new trials after being convicted in a wide-ranging murder and narcotics conspiracy prosecution. No one knows how often prosecutors engage in such duplicity but aren't caught. And even when prosecutors are caught, findings of misconduct aren't filed in an easily accessible directory. The legal system keeps track of convictions won, not convictions lost on appeal because prosecutors went too far. In a 1963 case, Brady vs. Maryland, the U.S. Supreme Court ruled that prosecutors must disclose evidence favorable to a defendant.
Courts use a similar threshold in cases where prosecutors presented evidence they knew to be false.
The result is that courts frequently uphold a conviction even when prosecutors suppress evidence or allow witnesses to lie, ruling that the prosecutor's actions, while reprehensible, probably did not change the trial's outcome. And catching prosecutors who have engaged in such deception can be extremely difficult. In the case of James Richardson, a Florida man wrongly convicted in the poisoning deaths of his seven children, certain evidence undermining the state's case surfaced only after being stolen from a prosecutor's office by a man dating the prosecutor's secretary. Richardson was set free in 1989 after serving 21 years. Evidence has surfaced in other cases only after a judge directed the U.S. marshal to seize the prosecutors' documents, or because newspapers sued under the Freedom of Information Act, or because of anonymous tips, conversations accidentally overheard, or papers spied in a prosecutor's hand.