Joseph Rudolph Wood execution: At least 2 full doses of lethal cocktail administered

Arizona executioners had to administer at least two full doses of a two-drug lethal injection cocktail to a convicted killer before he finally succumbed nearly two hours after his execution began, the state's assistant attorney general said on Thursday.

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Attorneys for the 55-year-old double murderer, who they said gasped and struggled for breath for more than 90 minutes during Wednesday's execution, demanded an independent probe into a procedure they said was cloaked in secrecy and then horribly bungled.

Arizona's governor has promised an internal review, but said justice had been done with the execution of Joseph Wood. State corrections officials pushed back against any suggestion the procedure was botched, saying Wood was fully sedated and never felt any pain.

"The IV team, which includes a licensed medical doctor, verified multiple times during the procedure that the inmate was comatose and never in pain," Charles Ryan, director of Arizona's Department of Corrections, said in a statement.

The complications in putting Wood to death, which came after two other lethal injections went awry earlier this year in Ohio and Oklahoma, renewed debate over the U.S. death penalty and prompted the state to suspend further executions pending an internal review.

An Arizona Republic reporter who witnessed the execution said Wood, who was the fifth person put to death in Arizona in the past two years, gasped 660 times before falling silent.

Assistant Attorney General Jeffrey Zick told Reuters that Wood was given at least two full doses of the lethal injection cocktail during the procedure at a prison southeast of Phoenix.

During an emergency hearing conducted mid-execution at the request of defence lawyers, Zick told a judge that the condemned man was unconscious and having an "involuntary" reaction, according to a transcript provided by defence attorneys.

"That involuntary reaction continues, but I am told that Mr. Wood is effectively brain dead and that this is the type of reaction that one gets if they were taken off life support," Zick said, according to the transcript. "The brain stem is working but there's no brain activity."

Wood was found guilty in 1991 of fatally shooting his former girlfriend Debbie Dietz, 29, and her father, Gene Dietz, 55, two years earlier at a Tucson automobile body shop.

'Bungled execution'

Defence lawyers, in demanding an outside review into what they say was "the most prolonged bungled execution in recent history," want to determine in part which drugs were used and in what amounts.

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"It is important for the people of Arizona to get answers, and only an independent investigation can provide the transparency needed following an execution cloaked in secrecy that went wrong," defence attorney Dale Baich said.

He said later he had no information about the second dose of drugs given to his client: "It appears from what the AG said that at least a second dose was administered. We expect this information to come out during an independent investigation."

A spokesman for Brewer said the governor was confident that an internal probe, which was expected to take several weeks, would be adequate.

States that impose the death penalty have scrambled to find new suppliers of chemical combinations for lethal injections after European drug makers objected to having their products used for that purpose.

In Ohio, a death row inmate took 25 minutes to die and reportedly convulsed and gasped for breath in January after he was injected with a deadly sedative-painkiller mix of midazolam and hydromorphone, the first such combination used for a lethal injection in the United States.

In Oklahoma in April, another convicted killer writhed in pain as a needle became dislodged during his execution. The process was halted, but the man died of a heart attack.

Arizona had said it would use the same combination of drugs that were used in Ohio but at higher doses.

The Arizona Republic urged Brewer to put a moratorium on further executions, saying a firing squad would be more humane than allowing a condemned inmate to gasp for breath for two hours.