Oklahoma's first execution in 6 years ends with inmate vomiting and convulsing before his death

• Oklahoma inmate John Marion Grant was executed by lethal injection on Thursday.
• Witnesses said Grant convulsed and vomited before his death.

Oklahoma's first execution in six years ended with the inmate, John Marion Grant, convulsing and vomiting before his death by lethal injection.

Witness to the execution KOKH reporter Dan Snyder said on Twitter that there were "repeated convulsions and extensive vomiting" from Grant for 15 minutes, despite the Oklahoma officials saying the execution was carried out "without complication."

Oklahoma had previously paused executions after two botched lethal injections in 2014 and 2015.

Clayton Lockett died in 2014 after a lethal injection execution left him writhing in pain for 43 minutes, according to HuffPost. In 2015, Charles Warner said his body was on "fire" during a lethal injection, HuffPost reported.

Grant was exerting with the same three-drug combination as Lockett.

He fell unconscious 15 minutes after the the first drug, the sedative midazolam, was injected, and was pronounced dead six minutes later, the Associated Press reported.

Grant was sentenced to die in 1999, after he killed prison cafeteria worker Gay Carter by stabbing her 16 times with a homemade shank while he was serving a 130-year sentence for several armed robberies.

An appeals court put a stay of execution in place for Grant and another death row inmate, Julius Jones, on Wednesday, but officials went through with Grant's execution after the Supreme Court lifted the stays.

Before Grant was killed, US District Judge Stephen Friot had said Grant's lethal injection could be used as evidence in a lawsuit about Oklahoma's lethal injection protocol, HuffPost reported.

Robert Dunham, the executive director of the Death Penalty Information Center, told HuffPost that Grant's situation became a "human experiment for other death-row prisoner's challenge to Oklahoma execution process."