A Native American man convicted of murdering a college student more than four decades ago was to be put to death Wednesday in Arizona, marking the southwestern US state's first execution since 2014.
Clarence Dixon, 66, was scheduled to receive a lethal injection in Florence State Prison at 10:00 am (1700 GMT). He would become the sixth person executed this year in the United States, according to the non-profit Death Penalty Information Center.
His lawyers have filed multiple appeals, arguing their client, who is blind, is suffering from paranoid schizophrenia and does not know why he faces capital punishment.
"Mr. Dixon really doesn't understand the claim because he lives in his head.... He lives in these alternate realities," lawyer Eric Zuckerman said Tuesday at a hearing before a San Francisco court which rejected his appeal.
A final request for a stay of execution was denied on Wednesday by the US Supreme Court.
Dixon stabbed, raped and strangled 21-year old student Deana Bowdoin in Tempe in January 1978, just days after being found not guilty of a different attack because of his psychological state.
Later he was sentenced to life in prison for a separate sexual assault in 1986, and through DNA testing he was linked to and convicted of Bowdoin's killing.
The execution will be Arizona's first after an eight-year hiatus following the botched execution of an inmate who suffered agonizing convulsions for two hours as he was injected with 15 doses of a chemical cocktail before he died.
Doubts about the legality of lethal injections -- suspected of causing unlawful suffering -- abound, and pharmaceutical companies have begun refusing to supply the chemicals, leading to a sharp nationwide decline in executions.
Officials in the state, where 113 prisoners including Dixon are on death row, have also authorized the gas chamber for carrying out capital punishment.
Arizona prison authorities are considering using hydrogen cyanide, the main component of Zyklon-B, a chemical infamously associated with the Holocaust.
Dixon was offered a choice of lethal injection or the gas chamber. His silence meant he was due to be given a lethal injection.
Arizona has set June 8 for the execution of Frank Atwood, sentenced to death in 1987 for the murder of an eight-year-old girl. He has been given two weeks to choose between lethal injection or being gassed with lethal chemicals.