An independent autopsy on an Oklahoma death row inmate found that he actually died of his lethal injection, not of a heart attack as officials first claimed. Clayton Derrell Lockett was pronounced dead of a heart attack by officials from the state Corrections Department 43 minutes after his execution began on April 29. Although the autopsy concluded that Lockett did not die from a heart attack, it did not determine why his execution took so long. It was an especially gruesome one: Lockett needed to be stunned, and medical officials struggled to find a suitable vein, eventually inserting the line through the femoral vein in his groin. Lockett was one of the botched executions that have occurred this year as state’s scramble to find substances to use for lethal injections, often turning to less reliable sources.