The Oklahoma Department of Public Safety released the autopsy findings for what has become one of the most notorious executions this year. Oklahoma, which planned to execute a second man the same night Lockett was put to death, has extended a moratorium into next year.
"It is our opinion that Clayton Derrell Lockett, a 38-year-old black male, died as the result of judicial execution by lethal injection," the report said.
Lockett was executed April 29 for raping and killing Stephanie Neiman of Perry, Okla., in 1999. Neiman, 19, was buried alive after a bungled home invasion.
An untested three-drug cocktail was used and the drugs administered through a vein in Lockett's groin, because corrections officials could not find a good one in his arms or legs. Robert Patton, the state director of corrections, decided to stop the drugs about half an hour after the first one was administered, but Lockett died more than 10 minutes later.
At the time, officials said he appeared to have had a heart attack.