An Arizona man convicted of killing a college student in 1978 is scheduled to become the first person to be executed in the state after a nearly eight-year hiatus in its use of the death penalty.

Clarence Dixon, 66, is scheduled to die by lethal injection on Wednesday morning at the state prison in Florence for killing 21-year-old Arizona State University (ASU) student Deana Bowdoin.

If the execution goes ahead as planned, he will be the sixth inmate to be put to death in the United States this year.

In recent weeks, Dixon’s lawyers have made arguments to the courts to postpone his execution, but judges had so far rejected the claim that he is mentally unfit to be executed and has no rational understanding of why the state wants to put him to death.

Dixon declined the option of being executed in the gas chamber — a method that has not been used in the US in more than two decades — after Arizona refurbished its gas chamber in late 2020.

Instead, the state plans to execute him with an injection of pentobarbital.

The state’s hiatus in executions was driven by an execution that critics say was botched and the difficulty of finding lethal injection drugs.

The last time Arizona used the death penalty was in July 2014, when Joseph Wood was given 15 doses of a two-drug combination over two hours.

Wood gasped more than 600 times before he died.

States including Arizona have struggled to buy execution drugs in recent years after US and European pharmaceutical companies began blocking the use of their products in lethal injections.

Authorities said Ms Bowdoin, who was found dead in her apartment in Tempe, was raped, stabbed and strangled with a belt.

Dixon, who was an ASU student at the time and lived across the street from Ms Bowdoin, was charged with raping Ms Bowdoin, but the charge was later dropped on statute-of-limitation grounds.

He was convicted, though, of killing her.

In arguing their client is mentally unfit, Dixon’s lawyers said he erroneously believes he will be executed because police at Northern Arizona University wrongfully arrested him in a previous case — a 1985 attack on a 21-year-old student.

His lawyers concede he was in fact lawfully arrested then by Flagstaff police.

Dixon was sentenced to life sentences in that case for sexual assault and other convictions.

DNA samples taken while he was in prison later linked him to Ms Bowdoin’s killing, which had been unsolved.

Prosecutors said there is nothing about Dixon’s beliefs that prevents him from understanding the reason for the execution and pointed to court filings that Dixon himself made over the years.

Defence lawyers said Dixon has been diagnosed with paranoid schizophrenia on multiple occasions, has regularly experienced hallucinations over the past 30 years and was found not guilty by reason of insanity in a 1977 assault case in which the verdict was delivered by then-Maricopa County superior court judge Sandra Day O’Connor, nearly four years before her appointment to the US supreme court.

Ms Bowdoin was killed two days after the verdict, according to court records.

Another Arizona death-row prisoner, Frank Atwood, is scheduled to be executed on June 8 for the killing of eight-year-old Vicki Lynne Hoskinson in 1984.

Authorities said Atwood kidnapped the girl, whose body was found in the desert north-west of Tucson.

Arizona has 113 prisoners on death row.