Oklahoma death row inmate, Clayton Lockett, died of a heart attack this past Tuesday during what appears to be a botched execution. Director of Oklahoma’s Department of Corrections, Robert Patton, said he halted the execution after Lockett’s vein “exploded” and he began to go into convulsions. The planned execution of Charles Warner has been postponed for two weeks following the mishap with the state’s three lethal injection drugs.

Back in 2000, Lockett was convicted of first-degree murder, first-degree rape, kidnapping, and robbery following the shooting death of 19-year-old Stephanie Nieman. He was also convicted of the rape and murder of his ex-girlfriend’s 11-month-old daughter which took place in 1997, CNN reported. Both Lockett and Warner questioned the Department of Corrections’ decision to withhold the source of the lethal injection drugs that were set to be used for their executions.

Ten minutes after Lockett was given the first drug that is intended to leave the inmate unconscious, midazolam, witnesses to the execution said he started to go into convulsions while writhing on the death chamber’s gurney. Although prison officials claim Lockett was unconscious 10 minutes after receiving the first injection, witnesses also say the curtains were closed to the execution and the inmate had shouted out three muffled statements.

"There was some concern at that time that the drugs were not having the effect, so the doctor observed the line and determined that the line had blown," Patton told reporters. "I notified the attorney general's office, the governor's office of my intent to stop the execution and requested a stay for 14 days for the second execution scheduled this afternoon."

Two other drugs included in the lethal injection cocktail, vecuronium bromide and potassium chloride, were administered at 6:30 p.m. Patton told the press on hand for the execution that vein failure had prevented the drugs from having their desired effect. Forty-three minutes after the start of execution, Lockett experienced a heart attack and was pronounced dead at 7:06 p.m.