Police were called to the trailer park in Marion, Pennsylvania, by Tammy Lynn Felbaum, born Tommy, who said that her husband had taken a drugs overdose. He died within an hour of being taken to hospital.

The doctors assumed that James Felbaum had suffocated on his vomit, although they saw a small surgical cut in his scrotum. A post-mortem examination revealed that he had died from blood loss after being castrated.

Mrs Felbaum, 42, told police that her husband had tried to castrate himself as the first step in a do-it-yourself sex-change operation. She knew that he was not doing it properly because she had undergone such an operation 20 years ago, so got her husband to write a consent note for her to perform the operation. After consulting books on anatomy and surgery, she set to work.

Mrs Felbaum is charged with homicide, aggravated assault, reckless endangerment and unauthorised practise of medicine and surgery.

Timothy McCune, the Butler County District Attorney, said: “You can’t consent to a medical procedure being performed on you by someone who’s not a medical doctor.” He said that the Felbaums’ caravan was not a suitable operating theatre because it lacked heat and water and was filled with waste from their two dogs, five cats and three birds.

Mr McCune said he did not believe that Mrs Felbaum intended to kill her husband and that, if the case went to trial, he would seek a conviction for involuntary manslaughter. She might evade prosecution altogether if psychiatric reports decided that she was not fit to stand trial.

“If it is against the law to drive a vehicle under the influence of marijuana, surely it must be at least equally offensive to allow a judge in a similar condition to preside over a capital trial,” Judge Stephen S. Trott said in the 9th Circuit Court of Appeals, which presides over appeals in the nine western states.

Warren Summerlin was convicted of murdering a woman with an axe in 1981 in Tempe, Arizona. The appeal court ruling means that his sentence will be reviewed if it is shown that the discretion of Judge Philip Marquardt, who presided over the trial, was impaired by marijuana.

In 1991 Judge Marquardt pleaded guilty to marijuana possession in Texas and admitted to being under the influence of the drug regularly since 1975. It was Marquardt’s second marijuana conviction. He later stepped down from the bench and was disbarred.

“Summerlin had a clearly established constitutional right in 1982 to have his trial presided over and his sentence of life or death determined by a judge who was not acting at that time under the influence of, or materially impaired by, a mind-altering illegal substance, such as marijuana,” Judge Trott said in his written judgment.

In a dissenting minority opinion, Judge Alex Kozinski said: “We have no indication, even as of the time of Judge Marquardt’s conviction, whether this addiction involved hourly, daily or weekly use of the drug, nor do we know whether it had become progressively worse over the years. There is nothing to suggest that the addiction affected Marquardt’s judgment or interfered in any way with his judicial duties.

Judge Kozinski feared that the judgment would result in “fishing expeditions” into judges’ private lives and habits and that if marijuana use by American judges was widespread it would “open the floodgates to similar claims by — quite literally — tens of thousands of state and federal prisoners”.

Judge Kozinski said Summerlin should have offered proof that the judge’s smoking of marijuana had influenced his murder conviction.

He might have “presented affidavits from those who observed the trial to the effect that Judge Marquardt was seen staggering when mounting or leaving the bench; that he had a glazed stare during the proceedings; that he had trouble comprehending arguments; that he fell asleep in court”.

However, Judge Trott said: “If Judge Kozinski’s speculation about the vulnerable state of the judiciary should surprisingly turn out to be correct and that our benches are indeed occupied by judges against whom similar cases involving illegal drug usage and addiction can be made, this would seem to be an argument in favour of an inquiry, not a reason to look the other way.”

He said that “we should not similarly tolerate a single drug-addicted jurist whose judgment is impaired, especially in a case involving life-and-death decisions.”

The primary legal precedents cited by Judge Trott for his decision were from cases involving the competency of juries, starting with a US Supreme Court decision from 1912, which held that a defendant was entitled to a post-trial hearing after questions were raised about the sanity of a juror.