Jury selection is under way for a unique trial in the US - to decide whether a man is intelligent enough to be executed.
Daryl Atkins' IQ has improved
Daryl Atkins will be put to death if the jury decides he is not retarded - and spared if it says he is.
Atkins' case led to the US Supreme Court in 2002 outlawing the execution of the mentally retarded.
But prosecutors argue his IQ has since increased, and that he can therefore be put to death.
"This case is going to be unique in the annals of judicial history," Judge Prentis Smiley told 70 potential jurors in Yorktown, Virginia.
He said Atkins "must prove he is mentally retarded by... a preponderance of the evidence".
If he failed to do so, another court had already decided his fate, he explained.
The trial is scheduled to last two weeks, and could hear from up to 100 witnesses.
The case is the latest battleground for those arguing for and against state-sanctioned executions in America
Atkins has twice been sentenced to death for the murder of a 21-year-old airforce man in 1996.
His lawyers successfully argued at the Supreme Court that executing the mentally retarded was unconstitutional.
But the court's ruling may not save his life.
The court left it up to individual states to define "retarded".
Virginia requires an inmate to have had an IQ of 70 or less, combined with poor social skills by the age of 18.
Atkins, 27, was not tested as a youth but he scored 59 in 1998, and 76 more recently.
The BBC's Oliver Conway, in Washington, says the jury must decide whether that improvement in IQ shows he is fit to be executed, or is merely the result of the mental stimulation gained from following his case.