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
In their research, Gross and his colleagues examined the 7,482 U.S.
death sentence convictions between 1973 and 2004.
Of those, 117 had been exonerated in recent years, thanks to the
efforts of numerous groups and a tide of public attention to issues
surrounding the death penalty.
Gross and his co-authors, Barbara O'Brien of Michigan State
University, Chen Hu of the American College of Radiology Clinical
Research Center in Philadelphia and the University of Pennsylvania's
Edward H. Kennedy, estimated that about 4 percent of those sentenced
to death were actually innocent, nearly three times the number
exonerated during that period.
For their conclusion, the research group used a mathematical formula
that included the number of inmates whose sentences were commuted to
life imprisonment, the length of time it took for a convicted inmate
on death row to be set free, and the number of inmates who were in
the end exonerated.
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In a twist, once inmates' sentences are commuted to life, they are
far less likely to be exonerated, mostly because there are fewer
legal resources given to their cases, Gross said.
"If you were never sentenced to death, you never had the benefit — if you call it a benefit — of that process," he said.
Although the study focuses on a period ending 10 years ago, the
percentage of false death sentence convictions likely holds true
today, Gross said.
The study does not say how many innocent people were likely put to
death. It also does not suggest that the rate of false convictions
in death sentence cases is the same as in any other conviction
(Reporting by Laila Kearney; editing by Sharon Bernstein and Paul Tait)
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