OKLAHOMA CITY (AP) -- An autopsy on an Oklahoma inmate who died after his troubled execution was halted concluded that he was killed by the lethal drugs, but it doesn't explain why he writhed, moaned and clenched his teeth before he was pronounced dead about 43 minutes after the process began.
Department of Corrections Director Robert Patton had said earlier that Clayton Lockett died from an apparent heart attack 10 minutes after Patton had halted the execution. But an independent autopsy released Thursday concluded that the cause of death was "judicial execution by lethal injection."
It hadn't been clear whether all three execution drugs administered to Lockett had actually made it into his system, but the autopsy determined that they did.
The autopsy was done by the Southwestern Institute of Forensic Sciences at Dallas, at the behest of the Oklahoma Department of Public Safety.
Dale Baich of the Federal Public Defender's Office in Phoenix, who represents a group of Oklahoma death row prisoners who commissioned an independent autopsy of Lockett, said more information is needed.
"What this initial autopsy report does not appear to answer is what went wrong during Mr. Lockett's execution," Baich said in a statement.
Oklahoma and other death penalty states have encountered problems in recent years obtaining lethal injection chemicals after major drugmakers stopped selling them for use in executions. That has forced states to find alternative drugs, purchased mostly from loosely regulated pharmacies that custom-make medications. Many states refuse to name suppliers and offer no details about how the drugs are tested or how executioners are trained.
Oklahoma put executions on hold after Lockett's April 29 execution.
Officials at the Oklahoma State Penitentiary in McAlester have said Lockett's vein collapsed during the lethal injection process. The autopsy does not say whether that's the case, though it does confirm that medical technicians poked him about 12 times as they tried to find a vein before settling on using one in his groin.
Gov. Mary Fallin has ordered public safety officials to review the events surrounding Lockett's execution, including state execution protocols that had been changed in the weeks ahead of it. The state Court of Criminal Appeals agreed to not schedule executions for six months. Three are set for November and December.
A spokesman for Fallin, Alex Weintz, said the autopsy report will be part of the full review. "We suspect they are in the final stages of that process," Weintz said.
He said Fallin still supports use of the death penalty. "But we want our executions to be successful," Weintz said, adding that Fallin asked the Oklahoma Department of Public Safety to recommend possible changes to the execution procedures.
The autopsy report does not include any recommendations about the protocols.
A spokesman for the Corrections Department, Jerry Massie, said prison officials will have no comment until after public safety officials release their findings and recommendations.
In Lockett's execution, Oklahoma used the sedative midazolam for the first time. The drug was also used in lengthy attempts to execute an Ohio inmate in January and an Arizona prisoner last month. Each time, witnesses said the inmates appeared to gasp after their executions began and continued to labor for air before being pronounced dead.
Midazolam is part of a three-drug and a two-drug protocol in Oklahoma. Lockett's execution used a three-drug protocol -midazolam, vecuronium bromide and potassium chloride. The state also has a protocol that would use midazolam with hydromorphone, the same combination used in the problematic executions in Ohio and Arizona this year.
Toxicology reports said all three lethal drugs were found in Lockett's system - the sedative in brain tissue and elsewhere and the other drugs in his blood.
A June lawsuit against the Department of Corrections on behalf of 21 Oklahoma prisoners alleged that prison officials are experimenting on death row inmates and violating the U.S. Constitution's ban on cruel and unusual punishment by tinkering with the state's lethal injection procedures. The state says those claims are false.