UPDATE | Autopsy underway after botched Okla. execution

OKLAHOMA CITY (AP) — Oklahoma officials are conducting an autopsy of a death row inmate who convulsed violently during his botched execution before he apparently died of a massive heart attack.

Medical examiner's spokeswoman Amy Elliott says the autopsy on 38-year-old Clayton Lockett was being performed today in Tulsa.

During his execution Tuesday evening that used a new sedative in a three-drug combination, Lockett gritted his teeth, tried to lift his head and convulsed violently after he had already been declared unconscious by a doctor. The state's prison director then halted the execution, and Lockett died later.

Elliott said the coroner will examine the body, including the sites where the drugs were administered, and conduct a toxicology report to determine the cause and manner of death.