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Arizona executioners had to administer 15 doses of a lethal drug cocktail before Joseph Wood finally died last month after gasping for two hours, state documents showed Friday — documents in which the state said the execution complied with the law.

The state Department of Corrections made the startling disclosure in a statement Friday announcing that it was proceeding with plans to appoint an independent panel to review Wood's execution July 23, using a never-before-tried cocktail of drugs from a source the state wouldn't disclose.

"A total of 750 mg each of Midazolam and Hydromorphone were administered to inmate Wood during the execution process," Charles Ryan, the department's director, said after 331 pages of documents were released to Wood's legal team.

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Those are the same drugs that Ohio used in January to execute Dennis McGuire, who seemed to struggle for air and took 25 minutes to die. Arizona, Ohio and other states have been trying new combinations of drugs from controversial compounding pharmacies because manufacturers have started refusing to sell them the drugs most commonly used in U.S. executions, typically potassium chloride.

Arizona's execution protocol (PDF), which was revised in March as the state looked for alternatives, specifies "an intravenous injection of a substance or substances in a lethal quantity sufficient to cause death."

The specific injection is prescribed as one mixing 50 milligrams of midazolam and 50 milligrams of hydromorphone — meaning Wood had to receive 15 doses to take in the 750 milligrams of each drug that the state disclosed for the first time Friday.

"These records indicate the length of the procedure and the amount of drugs administered comply with the department's mandate under state law," Ryan said.

But Dale Baich, Wood's federal public defender, said that because the state needed 15 times the drugs specified in the regulations to kill Wood, the records indicated just the opposite.

Of Ryan's contention that the dosage was legal, Baich told NBC News: "I think that was made up on the fly."

The Corrections Department and state attorney general's office didn't immediately respond to requests for comment late Friday afternoon.

Baich was rebuffed in a lawsuit before Wood's execution seeking to compel the state to reveal what the mix of drugs would be. By going ahead with an untested mix that was kept secret until Friday, he said, the state of Arizona conducted an "experiment" on an unwilling subject, and "it now appears that the experiment failed."

Media witnesses said Wood, who was condemned to death for the 1989 murder of his 29-year-old girlfriend, Debra Dietz, and her father — gasped for air more than 600 times for an hour and 40 minutes.

"At a certain point, you wondered if he ever was going to die," one of the witnesses said.