Michael Morales had been due to be executed at 12.01am (0801GMT) on Tuesday morning at California's San Quentin prison.

However, the sentence was initially postponed after anaesthesiologists required for the lethal-injection procedure refused to take part based on moral concerns.

Officials then rescheduled the execution for 15 hours later, planning to carry out the sentence using a single lethal dose of sedatives.

That too was eventually called off after it became clear that they could not find a medical expert willing to administer the dose, as ordered by a federal judge.

The anaesthesiologists had been brought in after Morales' lawyers argued that the three-part lethal injection process violated the Eighth Amendment prohibition against cruel and unusual punishment in the US constitution.

"Any such intervention would clearly be medically unethical"

Statement from anaesthesiologists

The lawyers said a prisoner could feel excruciating pain from the last two chemicals if he were not fully sedated.

The two anaesthesiologists who were going to be present objected to that they might have to advise the executioner if the inmate woke up or appeared to suffer pain.

'Unethical'

Opponents of the death penalty
have welcomed the delay

"Any such intervention would clearly be medically unethical," the doctors, whose identities were not released, said in a statement. "As a result, we have withdrawn from participation in this current process."

A week earlier, in response to Morales' lawyers, US District Judge Jeremy Fogel had given prison officials a choice: bring in doctors to ensure Morales was properly anaesthetised, or skip the usual paralysing and heart-stopping drugs and execute him with an overdose of a sedative.

Following the initial delay when the anaesthesiologists refused to take part, prison officials had planned to press forward with the execution on Tuesday night using the second option.

Fogel approved that decision, but said the sedative must be administered in the execution chamber by a person licensed by the state to inject medications intravenously.

It subsequently became clear that prison officials could not find any such medical professional and as a result the prison warden decided to "stand down" the execution.

"We are unable to have a licensed medical professional come forward to inject the medication intravenously, causing the life to end," Vernell Crittendon, a spokesman for San Quentin State Prison said.

Delay

California has executed 14
inmates since 1978

It was unclear when Morales' execution would now be carried out, but the delay could last for months because of legal questions surrounding California's method of lethal injection.

The incident has renewed a long-standing ethical debate about the proper role of doctors in executions and the suitability of the lethal injection method used in California and 35 other states.

The American Medical Association, the American Society of Anaesthesiologists and the California Medical Association all opposed the anaesthesiologists' participation as unethical and unprofessional.

Morales himself was moved off death row pending a court hearing expected in early May on the mechanics of the lethal injection process.

Morales was sentenced to death in 1983 for killing 17-year-old Terri Winchell, who was attacked with a hammer, stabbed and left to die half-naked in a vineyard.

"It feels like we just got punched in the stomach"

Barbara Christian,
Mother of murder victim

Winchell's mother, Barbara Christian, said she was outraged by the repeated delays in carrying out the execution.

"I'm totally disillusioned with the justice system. We've been waiting 25 years with the expectancy that he is gonna pay for his crimes," she said.

"It feels like we just got punched in the stomach."