TUCSON, Ariz. — Arizona executioners injected Joseph Rudolph Wood with a lethal combination of drugs 15 times during the nearly two hours it took for him to die, according to documents released Friday.

Records released to Wood’s attorneys show he was administered the sedative midazolam and the painkiller hydromorphone in 50-milligram increments 15 times between 1:53 p.m. and 3:45 p.m., for a total of 750 milligrams of each drug. He was pronounced dead at 3:49 p.m. after gasping more than 600 times while he lay on the table.

“Those are pretty staggering amounts of medication. They did not shortchange in the dose,” said Karen Sibert, a longtime anesthesiologist and spokeswoman for the California Society of Anesthesiologists.

Sibert, an associate professor at Cedars-Sinai Medical Center, said patients who are sedated before a surgery typically receive no more than 2 milligrams each of midazolam and hydromorphone.

“It would be rare that I would use more than 2 milligrams even for a lengthy surgery,” Sibert said. “If that is accurate, that is absolutely a lethal dose.”

Wood’s attorney, Dale Baich, said the dosage details show why an independent investigation of Wood’s execution by a nongovernmental authority is necessary.

“The Arizona execution protocol explicitly states that a prisoner will be executed using 50 milligrams of hydromorphone and 50 milligrams of midazolam,” he said in a written statement. “The execution logs released today by the Arizona Department of Corrections shows that the experimental drug protocol did not work as promised. Instead of the one dose as required under the protocol, ADC injected 15 separate doses of the drug combination, resulting in the most prolonged execution in recent memory.”

Wood’s July 23 execution renewed debate over the death penalty and the efficacy of lethal injection. It was the third execution to go awry in the U.S. this year.

An Ohio inmate gasped in similar fashion for nearly 30 minutes in January.

An Oklahoma inmate died of a heart attack in April, minutes after prison officials halted his execution because the drugs weren’t being administered properly.

Arizona officials say Wood, who was convicted of a 1989 double-murder, never suffered and was completely sedated. His attorney says it was a “horrifically botched execution” that should have taken 10 minutes.

Gov. Jan Brewer ordered a review of the state’s execution process, saying she’s concerned by how long it took for the drug protocol to kill Wood. The Arizona Department of Corrections said Friday it is seeking an outside investigator for the independent inquiry.

“I am committed to a thorough, transparent and comprehensive review process,” director Charles Ryan said in a news release. “This will be an authoritative review to ensure that fact-based conclusions are reached regarding every aspect of this procedure, including the length of time it took for the execution to be lawfully completed.”

Wood, convicted of killing ex-girlfriend Debbie Dietz and her father, Gene Dietz, in Tucson, took gasps for air for more than 90 minutes after officials administered the drugs.

His attorneys attempted to stop the execution after it was clear he was taking too long to die, but their efforts were not successful.

Ryan, the corrections chief, has denied that the execution was botched.