A convicted murderer who died in a botched execution last month in Arizona was injected with 15 separate doses of a drug combination because the initial drug protocol of one dose didn’t seem to be enough to kill him, according to documents released by the state Department of Corrections to the inmate's attorney.

The reports, released late Friday, are just the latest twist in the execution of Joseph Rudolph Wood III. Witnesses and his attorneys said Wood gasped and snorted for more than 90 minutes before he died; the incident prompted the governor to order an investigation and reinvigorated a national debate over the death penalty.

Wood, 55, was sentenced to death in 1991 for the August 1989 shooting deaths of his estranged girlfriend, Debra Dietz, and her father, Eugene Dietz, in Tucson.

Arizona Department of Corrections protocol calls for a prisoner to be executed with an initial dose of 50 milligrams of hydromorphone and 50 milligrams of midazolam but stipulates that more doses can be administered as long as the agency’s director gives the green light to do so. That was the case in this instance, said Doug Nick, a Department of Corrections spokesman.

Execution logs released to Wood’s attorney show that the initial experimental drug concoction wasn’t enough to kill him, leading officials to administer more drugs. On July 23, Wood received an injection at 1:52 p.m. at the Arizona State Prison Complex in Florence. The second dose was administered at 2:08 p.m., and more doses were injected at a rate of almost every couple of minutes until Wood was pronounced dead at 3:49 p.m.

The final five doses were administered while Wood’s lawyers were attempting to persuade a federal judge to stop the execution. The hearing with U.S. Judge Neil Wake, a conference call with the chief counsel of the Arizona attorney general's office, began at 3:27 p.m. The execution had been going on for more than an hour.

“The execution logs released today by the Arizona Department of Corrections shows that the experimental drug protocol did not work as promised,” Wood's attorney, Dale Baich, said in a statement.

The Department of Corrections refused to release a copy of the report to the Los Angeles Times but issued a statement defending the agency.

“These records indicate the length of the procedure and the amount of drugs administered comply with the department’s mandate under state law to administer … an intravenous injection of a substance or substances in a lethal quantity sufficient to cause death, under the supervision of the state Department of Corrections,” the statement said.

Some are questioning whether the investigation into Wood’s death should be done by the agency in charge of his execution.

“I feel the investigation should not be done by the Department of Corrections itself, but by an independent investigator who will thoroughly and impartially answer the questions of what happened and why,” said state Sen. Ed Ableser.

It took so long for Wood to die that reporters witnessing the execution counted several hundred of his wheezes before he was declared dead, nearly two hours after the procedure began.

The incident comes at a time of controversy over other botched procedures and secrecy about what drugs are used and in what combinations.

“I thought it was shocking,” said Deborah Denno, a professor at Fordham Law School and a death penalty expert, of the news that Wood received 15 doses.

“2014 has been a perversely banner year in botched executions,” Denno said Saturday. “It’s very disturbing. This is not a concocted problem by any means. This is a national concern right now.”

She noted that U.S. Atty. Gen. Eric H. Holder Jr. had said Thursday on PBS that although there is no legal requirement to disclose what drugs are used in executions, “transparency would be a good thing.”

John McAdams, an associate professor of political science at Marquette University, said opposition to the death penalty has been the cause of recent problems with lethal injections.

“We didn’t get stories like this for years and years until death penalty opponents pressured drug companies not to make available drug cocktails that were doing an effective job,” McAdams said Saturday. “They’re causing the trouble themselves and then they use the trouble they cause as argument against the death penalty.”

Arizona officials didn’t want to disclose where the state obtained the execution drugs because they wanted to protect the company from being bullied, he said.

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Times staff writer Maya Srikrishnan in Los Angeles contributed to this report.