A man who killed a police officer by shooting him twice in the back of the head should not be executed because he can no longer remember committing the crime, his lawyers have said.
Vernon Madison has suffered several strokes in recent years, resulting in dementia which has wiped out his memory of the 1985 murder of Julius Schulte.
The 67-year-old prisoner has spent decades on death row, is registered blind, cannot walk on his own and speaks with a slur, according to court documents.
He was supposed to be executed last month, but the procedure was halted by the US Supreme Court after an appeal by his lawyers, who argued "his mind and body are failing".
The court has now agreed to hear the case of the convicted killer from Alabama, whose lawyers say "killing a fragile man suffering from dementia is unnecessary and cruel".
They also argue that a judge should not have sentenced Madison to death when jurors recommended life imprisonment.
The case has divided the opinion of judges over the years.
In 2016, a state court ruled he was competent.
However later the same year, seven hours before he was due to be put to death by a lethal injection, the 11th US Circuit Court of Appeals halted the execution.
It ruled: "According to his perception of reality he never committed murder."
Last November, Supreme Court justices overturned that decision, allowing the state of Alabama to set a new execution date.
The Supreme Court has said death row prisoners must have a "rational understanding" that they are about to be executed and why.
It has previously imposed some limits on capital punishment relating to people with intellectual disabilities and mental illnesses.
Mr Schulte, a police officer in Mobile, Alabama, was responding to a call about a missing child made by Madison's then-girlfriend when he was killed.
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He was sat in his patrol car when, according to prosecutors, Madison crept up and shot him.
Michael Schulte, the dead officer's son, said last month the last-minute execution stays had been difficult for his family and meant "this tragedy isn't finished".