A US judge has said he will stop the execution of a prisoner, due next week, unless California state alters its method of killing by lethal injection.
Several US states use the lethal injection to execute convicts
Federal judge Jeremy Fogel wants new measures to ensure the lethal injection does not cause undue suffering.
Lawyers for Michael Morales say the mix of drugs used in the injection could mean he dies in extreme pain.
The judge wants a new mix, or an expert to be present, to ensure Morales is not conscious when the toxins take effect.
Judge Fogel said the Eighth Amendment of the US constitution forbade punishments "incompatible with the evolving standards of decency that mark the progress of a maturing society".
He also pointed to the recent execution of former Los Angeles gang boss Stanley Tookie Williams, whose death by lethal injection in December took several minutes.
The judge said he was concerned that a sedative administered to convicts might not always be enough to prevent them from feeling any pain from paralyzing and heart-stopping chemicals in the injection.
US METHODS OF EXECUTION
Lethal injection: Authorized in 37 states
Electrocution: In 10 states (sole method in Nebraska)
Gas chamber: In five states (all of which have lethal injection as alternative)
Hanging: Only in New Hampshire and Washington
Firing squad: In Idaho and Oklahoma
Prosecution and defence lawyers quoted by the judge acknowledged that the chemicals would be extremely painful to anyone awake enough to feel them.
Medical experts have however argued that the dose of sedatives is strong enough to make almost anyone unconscious within a minute.
Judge Fogel said California state must give convicts a fast-acting dose of barbiturates to ensure they are unconscious before the toxins are administered.
Alternatively, he said, a medical expert could be present to ensure they are not conscious.
If the state rejects his recommendations, Judge Fogel said he would postpone the execution and order court hearings into California's method of lethal injection.
Morales was sentenced to death after being found guilty of the rape and murder of a teenager in 1981.