WASHINGTON (AFP) - An American murderer died of a heart attack on Tuesday more than 40 minutes after his execution was halted due to a botched lethal injection, leading Oklahoma to postpone the execution of a second inmate.
Convicted murderer and rapist Clayton Lockett was administered a new, untested three-drug protocol that included a sedative, an anesthetic and a lethal dose of potassium chloride in what would have been the central state's first double execution in 80 years.
But Oklahoma Department of Corrections director Robert Patton ordered the execution of Lockett stopped about three or four minutes after the start of the injection at 6.23pm, citing a "vein failure", a prisons spokesman said.
Lockett died of a "massive heart attack" at 7.06pm after receiving all three drugs, spokesman Jerry Massie said. Even though he was administered the injection, "the drugs didn't go into the system", the spokesman added.
Mr Patton then immediately ordered a 14-day delay to the execution of Charles Warner, who had been set to be executed two hours later.
Oklahoma had previously postponed the two executions in March because of a shortage of lethal injection drugs.
But the state managed to get supplies, while changing the execution protocol, and the two inmates exhausted their appeals.
Lockett was convicted in 2000 for the rape and murder of a young woman he kidnapped, beat and buried alive.
Warner was convicted for the 1997 rape and murder of an 11-month-old girl.
Warner's lawyer Madeline Cohen had argued against the new injection combination, saying the "experimental new drug protocol, including a paralytic", would make "it impossible to know whether the executions will comport with the Eighth Amendment's ban on cruel and unusual suffering".
"Despite repeated requests by counsel, the state has refused, again and again, to provide information about the source, purity, testing and efficacy of the drugs to be used. It's not even known whether the drugs were purchased legally," she said.
Both Lockett and Warner had argued they had the constitutional right to know the composition and origin of any drugs used in the lethal injection.
In a judicial twist, Oklahoma's Supreme Court had first suspended the executions in order to resolve the controversy, but then two days later reversed itself, saying the men had no more right to information on drugs than they would for the electric chair.
Since European manufacturers began refusing to sell the most commonly used anesthetic - pentobarbital - for human executions, several US states have found themselves confronted with shortages, and are now seeking an alternative, which has led to an increase in court cases over the issue.
The last time two inmates were executed on the same night in Oklahoma was in 1937.