Washington - A US man diagnosed with mental retardation will be executed on 18 July for killing a fellow prisoner, his lawyer said.
Warren Hill was sentenced to death in the southeastern state of Georgia, despite a US Supreme Court decision banning the execution of convicts with intellectual disabilities.
"Executing Warren Hill, a 52-year-old man whom a court has found to be more likely than not mentally retarded, would be a terrible miscarriage of justice," Hill's attorney Brian Kammer wrote on the Death Penalty Information Centre's website.
Kammer also defended another man on death row in Georgia, Troy Davis, whose 21 September execution sparked protests against capital punishment across the nation. Kammer will ask Georgian authorities to grant Hill clemency.
The US Supreme Court ruled against the execution of prisoners with mental disabilities in 2002, but has left each state with the authority to determine what constitutes mental disability. Georgia maintains mental retardation must be proved "beyond a reasonable doubt".
A Georgia judge ruled that Hill was intellectually disabled, but to a lesser degree than the state requires to preclude the death penalty.
In 2003, the Georgia Supreme Court determined that Hill's defence failed to prove his mental retardation beyond a reasonable doubt, and an appeals court upheld the ruling, "even if we believe it incorrect or unwise".
The US Supreme Court declined to review Hill's case, but his lawyers have requested that the matter be reconsidered.
Hill, who has spent 21 years on death row, was sentenced to death in 1991 for murdering a fellow prisoner. He was originally in prison for murdering his girlfriend, according to state authorities.
The prisoner reportedly has an IQ of 70, meeting the threshold for mental disability.
"Hill has endured a life of hardship and tribulation" with "an extensive family history of diminished intellectual capacity", Georgia Council on Developmental Disabilities chief Eric Jacobson told the Daily Report newspaper.
"He grew up in poverty in Elberton, Georgia, and survived chronic domestic violence at the hands of his mother and alcohol-dependent father."