McALESTER, Okla. (AP) — Oklahoma prison officials halted an inmate's execution after a new drug combination left him writhing and clenching his teeth on the gurney. He later died of a heart attack.

Thirty-eight-year-old Clayton Lockett was declared unconscious 10 minutes after the first of the three-drug combination was administered Tuesday. Three minutes later he began breathing heavily, writhing, clenching his teeth and straining to lift his head off the pillow.

The blinds were lowered to prevent those in the viewing gallery from watching. The state's top prison official eventually halted the proceedings.

Lockett died of a heart attack a short time later.

Gov. Mary Fallin ordered a 14-day stay of execution for death row inmate Charles Warner, who was scheduled to die two hours after Lockett.

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