An Oklahoma inmate whose execution was bungled in April, died as a result of lethal injection, a medical examiner has found.

Clayton Lockett, 38, was scheduled to die by lethal injection April 29. He writhed and convulsed on a gurney during the procedure and died 43 minutes after the execution began. His death sparked a national discussion over capital punishment and prompted President Obama to order a review of death penalty procedures.

According to an independent autopsy conducted at the Southwestern Institute of Forensic Sciences in Dallas, Lockett died “as the result of judicial execution by lethal injection.” Gov. Mary Fallin ordered the autopsy as part of an investigation into Lockett’s death.

The autopsy shows the extent to which medical personnel went to execute Lockett. Officilas have said a technician had trouble finding a suitable vein. There were more than 10 needle marks on Lockett’s body, including three to four near his jugular vein, two on his foot and one on his left wrist.

The execution was carried out after an IV was placed in Lockett’s groin. The autopsy notes hemorrhaging of the soft tissue under Lockett’s groin. That suggests that the IV may have been improperly placed; officials in April said that the drugs used in the execution may have pooled under Lockett’s skin. Officials said Lockett may have been dehydrated, but the autopsy found no evidence of dehydration.

At the time of Lockett’s death officials said Lockett died of a suspected heart attack, a claim that is not backed up in the autopsy, and that his vein apparently collapsed during the procedure.

An independent autopsy conducted earlier this year at the behest of attorneys for death row inmates in Oklahoma showed that execution team failed to properly place an IV. It also said Lockett’s veins had “great integrity,” despite assertions that they had collapsed.

Oklahoma officials said Lockett was Tasered the morning of his execution, but the autopsy said there were no Taser marks on his body.

Lockett was executed using a cocktail of drugs that Oklahoma was using for the first time. He was convicted of murder and other charges, including rape, in 2000 after he and two accomplices attacked two young women, one of whom Lockett shot twice. Lockett then ordered his accomplices to bury her alive, witnesses said.

Fallin ordered an independent investigation into Lockett’s death in the days after the execution. It is scheduled to be made public in the coming days.

Related: Everything you need to know about executions in the United States.