A new study that uses exonerations to try to measure how many prisoners with death sentences have been wrongly convicted has found that at least 4.1 percent would eventually be proven innocent and freed if kept on death row long enough. The study’s lead author Samuel Gross, a criminologist at the University of Michigan Law School, says that given enough time at least one in 25 prisoners would be released.
The study, which is one of the first to try to determine the rate of wrongful convictions, was led by a team of statisticians and lawyers who used exonerations as their method to try to get a hint of the scale of wrongful convictions. Although few convictions are overturned after the discovery of proof of innocence, even fewer prisoners with life sentences are exonerated because there is less chance of having the error discovered. It would appear more effort is put into proving innocence if it is a matter of life and death, since less than 0.1 percent of convictions are given death sentences, but up to 12 percent of exonerations between 1989 and 2012 took place in death sentence cases.
Data on 7,482 defendants with death sentences and pardons between 1973 and 2004 was studied, attempting to answer the question of how often a death row prisoner was found innocent and freed. According to Gross, the study used exonerations because it is the only way to get a hint of the magnitude of unjust convictions, and since the outcomes of prisoners with death sentences are carefully tracked by the U.S. Bureau of Justice Statistics in Washington DC.
Many death sentences are never carried out because they are changed to life in prison, or because the inmate dies from suicide or natural causes, so the study tracked only those with an end point of either exoneration or execution. Researchers then used statistics to figure out what would have happened to the prisoner if they had stayed on death row indefinitely. They found that the longer a person is there, the more their chances of being pardoned increase. It is more likely that people put to death quickly are innocent, since there has not been as much time for further evidence to be found.
The study finds that more than twice as many inmates are wrongly convicted and sentenced to death than have been exonerated and freed. Since 1973, 144 death row defendants have been exonerated in the U.S. Using a survival curve statistical method, commonly used in medicine to estimate death rates, the study’s analysis showed that at least 340 people would have been wrongly put to death in same time period.
James Liebman, a lawyer at Columbia Law School who was not involved in the study, says the statistics show something of a contradiction. Innocent people often plead guilty hoping to avoid death row, and some convicts are lucky enough to have their capital sentences commuted to life. But they may not actually be the lucky ones if they have been wrongly convicted, because prisoner exonerations are seen more often on death row than with life sentences.
By Beth A. Balen