Update: A Fulton County judge issued a stay of Hill's execution on Monday afternoon, according to the Atlanta Journal-Constitution.

State uses secret law to obtain lethal drug pentobarbital from compounding pharmacy as lawyers claim breach of eighth amendment

The state of Georgia was due to execute an intellectually disabled man on Monday, barring any last-minute legal intervention, in what would appear to be a clear violation of the eight amendment of the US constitution.

It is the third time that Warren Hill, 52, has faced execution in 12 months. He was spared death by lethal injection on 23 July last year and 19 February this year – with 90 minutes and 30 minutes respectively to go before the switch was pulled.

Now he is being prepared to be taken to the death chamber for a third time. He will have visits from his family, spend time with the prison chaplain and be offered a last meal.

His only hope rests with two legal challenges that have been brought by his lawyer Brian Kammer. The first is a habeus petition lodged last week with the US supreme court.

It points out that the supreme court itself banned executions of intellectually disabled prisoners – still known as "mentally retarded" in US jurisprudence – in 2002. In Atkins v Virginia, the court found that death sentences of intellectually disabled inmates ran the risk of exposing them to cruel and unusual punishment.

Hill's guilt is not in question. In 1990 he was already serving a life sentence for murdering his girlfriend when he killed fellow inmate John Handspike in a Georgia prison, beating him to death with a nail-studded board.

All nine medical experts who have examined Hill over the years are now in agreement that he is intellectually disabled. They include three doctors whose expert opinion in 2000 that the condemned man was not "retarded" was seminal in having him sent to his death – they now say that their initial view was rushed and based on outdated medical understanding.

The second legal challenge, put before Georgia state courts last Friday, concerns the new Lethal Injection Secrecy Law passed recently by the Georgia assembly that allows the department of corrections to obtain supplies of the sedative pentobarbital in secret. The legislation bypasses normal freedom of information rules by declaring the identity of drug suppliers a "state secret" in an attempt to circumvent a growing boycott of medical drugs used in executions.

The Georgia department of corrections is understood to be seeking pentobarbital to kill Hill through a compounding pharmacy, though it is using the new secrecy law to keep details of the supplier obscured. Hill's lawyer complains that as a result the prisoner is left "with no means for determining whether the drugs for his lethal injection are safe and will reliably perform their function, or if they are tainted, counterfeited, expired or compromised in some other way."

Kammer goes on to argue in the legal challenge that the uncertainty surrounding the drugs to be used to put him to death also constitutes another violation of the eighth amendment of the US constitution, rendering his pending execution this evening a singularly controversial event even by the standards of the US death penalty.

© Guardian News and Media 2013