A death row murderer has avoided execution for the seventh time after his lawyers argued the lethal injection is inhumane.

The legal team of Thomas Douglas Arthur, 74, told a court Alabama's death penalty is "excruciatingly painful" and causes "agonising effects".

But the reason for this latest stay of execution was not revealed in the court order.

Arthur had been on a prison work release program after an earlier murder when, on his girlfriend's request, he disguised himself as a black man and shot Troy Wicker in 1982.

Judy Wicker, wife of Troy, paid Arthur $10,000 for the murder and told police a black man raped her, knocked her unconscious and shot her husband at their home.

Limited crime scene testing found no DNA link to Arthur. Alabama lost a rape kit that might have cleared Arthur, his lawyers said.

Arthur's scheduled execution came after three trials and another inmate's confession to the crime. In all, Alabama had scheduled Arthur's execution six times before Thursday.

In 2008, prisoner Bobby Ray Gilbert confessed to killing Wicker but a state court held that Gilbert and Arthur had conspired to submit a fake confession.