Shudder. A new study estimates that one in every 25 prisoners on death row is innocent. The research, published in the Proceedings of the National Academy of Sciences, analyses the 1,320 executed defendants since 1977. It also finds that in the past 31 years, 1.6 percent of death sentence recipients have been exonerated and set free. Its authors notes that the majority of those sentenced to death are commuted to life imprisonment, and therefore don't factor into the calculation. They write that "the criminal justice system goes to far greater lengths to avoid executing innocent defendants than to prevent them from remaining in prison indefinitely."