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More than 4% of death row inmates may be innocent: Study

The lethal injection chamber at Eyman Prison in Phoenix, Ariz.
The lethal injection chamber at Eyman Prison in Phoenix, Ariz.

One in 25 inmates sentenced to death row are likely innocent, according to a study published this week.

Researchers found that there's a good chance that 4.1% of criminal defendants who are sentenced to death are wrongly convicted – and those are merely conservative calculations.

The study spanned more than three decades -- between 1973 and 2004 -- looking into all 7,482 death sentences during that time. The figures, gathered by the Justice Department and nonprofit group The Death Penalty Information Center, landed some eye-popping results. Only 1.6% of those people sentenced to death were exonerated, while an estimated 200 more inmates could have been cleared, but weren’t. Another 35.8% were removed from death row but remained in prison after their criminal convictions were either reversed or modified.

Calculating false conviction rates can be complicated matter. There are no reliable statistics or national database tracking most criminal cases, and many erroneous convictions go by unnoticed. Supreme Court Justice Antonin Scalia argued in 2006 that the false conviction rate is actually closer to 0.027%. Researchers behind the study -- titled "Rate of False Conviction of Criminal Defendants Who Are Sentenced to Death" -- smacked down the justice’s estimates, saying the actual rate is “far greater.” Many of those assumptions divide the number of total exonerations by the number of felony convictions, they said, calculations that don’t account for false convictions that are not unearthed.

“Our research adds the disturbing news that most innocent defendants who have been sentenced to death have not been exonerated, and many -- including the great majority of those who have been re-sentenced to life in prison -- probably never will be,” the researchers found.