As many as 300 people who were sentenced to death in the United States over a three-decade period were likely innocent, according to a study published in a leading science journal on Monday.
Dozens of defendants sentenced to death in recent years have been exonerated before their sentences could be carried out, but many more were probably falsely convicted, said University of Michigan professor Samuel Gross, the study's lead author.
"Our research adds the disturbing news that most innocent defendants who have been sentenced to death have not been exonerated," Gross wrote in the study, published in the Proceedings of the National Academy of Sciences.
However, he stressed that this did not indicate a jump in the number of people believed wrongly executed because some had had their sentences commuted to life imprisonment and others lingered on death row.
In their research, Gross and his colleagues examined the 7,482 U.S. death sentence convictions between 1973 and 2004.