A Texas man is due to be executed next month despite admissions by jurors that they consulted biblical passages advocating death as a punishment to help to decide his fate.

Before sending Khristian Oliver to his death after he was convicted of murdering his victim — who was bludgeoned with a gun barrel — jurors read passages of the Old Testament, including one that states that a killer who uses an iron object to kill “shall surely be put to death”. Oliver, 32, is due to be executed on November 5. He was convicted in 1999 of the murder of Joe Collins, 64, during a 1998 break-in at the victim’s rural East Texas home.

During the trial, the jurors were instructed by the judge not to refer to anything that was not presented as evidence in the courtroom.

Amnesty International called on the Texas authorities to commute Oliver’s death sentence because since his trial, jurors had admitted that they read the Bible while they decided whether he should live or die. In particular, they said that Bibles were passed around with specific passages highlighted, and that one juror read aloud to his fellow jurors the passage, from Numbers XXXV, 16: “And if he smite him with an instrument of iron, so that he die, he is a murderer: the murderer shall surely be put to death.”

Mr Collins was shot by Oliver and then repeatedly struck with a gun barrel.

In a post-trial hearing two months after Oliver was condemned to death, four jurors acknowledged to the judge that Bibles had been present in the jury room, and that highlighted passages were passed around.

In 2002 a Danish journalist interviewed a fifth juror, who said that “about 80 per cent” of the jurors had “brought scripture into the deliberation” and that they had consulted the Bible “long before we ever reached a verdict”.

The fifth juror also said that he believed “the Bible is truth from page one to the last page”, and that if civil law and biblical law were in conflict, the latter should prevail.

He added that if he had been told he could not consult the Bible, “I would have left the courtroom”. He described himself as a death penalty supporter, saying that life imprisonment was a burden on the taxpayer.

The 5th US Circuit Court of Appeals said last year that jurors had wrongly used the Bible and that it had amounted to an “external influence” prohibited under the US Constitution. Yet the court said there was not enough evidence to show they were prejudiced when they decided to send Oliver to death row.

In April the US Supreme Court — the final chance Oliver had to appeal against his death sentence — refused to hear the case, despite being urged to do so by 50 former and current federal and state prosecutors. Kate Allen, the British director of Amnesty, called the use of the Bible in the juror’s deliberations “deeply, deeply troubling”.

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