By Matt Pearce, Molly Hennessy-Fiske and Paresh Dave, Los Angeles Times

A controversial double execution in Oklahoma was called off Tuesday night after the first inmate to receive an experimental three-drug cocktail writhed and grimaced on the gurney, struggled to lift his head and died of a heart attack more than 40 minutes later, officials and witnesses said.

Clayton Lockett’s botched death occurred after a constitutional showdown over Oklahoma’s execution secrecy laws. It is likely to provoke strong criticism from death penalty opponents at a time when similar policies on lethal injections have come under attack.

The incident will have a huge effect, said Deborah W. Denno, a professor at Fordham University School of Law and a death penalty expert. “The entire world was watching this execution.”

According to reporters at the scene, Lockett, 38, received the first dose of the three-drug cocktail at 6:23 p.m. The drugs included midazolam, which causes unconsciousness; vecuronium bromide, which stops respiration; and potassium chloride, which stops the heart. They are administered in that order. The state has said the procedure is meant to involve three doctors with hand-held syringes, injecting the drugs into IV lines in both arms.

At 6:33 p.m., 10 minutes after the injections, a doctor said Lockett was unconscious. But three minutes later, he began to nod and mumble and writhe, witnesses said.

The following account of Lockett’s death was tweeted after the fact by Associated Press and Tulsa World reporters at the execution.

He was conscious and blinking, licking his lips even after the process began. He then began to seize. — Bailey Elise McBride

Prison officials said they will try to get Lockett to hospital to resuscitate him. — Bailey Elise McBride

Clayton Lockett died inside the execution chamber at 7:06 pm of a massive heart attack according to DOC officials. — Cary Aspinwall

The Oklahoma Department of Corrections confirmed that Lockett did not die immediately. Director Robert Patton “did say that it appears that a vein (of Lockett’s) blew up or exploded, it collapsed, and the drugs were not getting into the system like they were supposed to,” spokesman Jerry Massie said.

The condemned man “was obviously showing some movement” after the injection, Massie said.

“After several minutes, five minutes, he was not unconscious,” he said. “They made a decision to halt the execution, but at 7:06 he suffered a massive heart attack and expired.”

Oklahoma Gov. Mary Fallin had strongly pushed for Tuesday night’s double execution. In a statement, she acknowledged the botched death and ordered a two-week delay in the execution of Charles F. Warner, who was to die after Lockett.

“I have asked the Department of Corrections to conduct a full review of Oklahoma’s execution procedures to determine what happened and why during this evening’s execution of Clayton Derrell Lockett,” Fallin said.

Lockett was convicted of murdering a woman in 1999. Warner was convicted of killing his girlfriend’s infant daughter in 1997.

One of Lockett’s attorneys, Dean Sanderford, witnessed the execution from the same room as the reporters. Lockett’s movements started as twitching and ended like a seizure, he said. “What we saw is somebody coming back to consciousness.”

Then the blinds went down and the microphone in the death chamber was turned off.

“Exactly what we were worried about happened,” he said. “He died in pain.”

Warner’s attorney, Madeline Cohen, called Lockett’s death “horrible and certainly something we hope and pray will never happen.”

“Our feeling right now is that until there is a full investigation, including an independent autopsy and full transparency about the drugs, Oklahoma should not be executing anybody else,” said Cohen, who was not in the observation room. “We will take all possible legal steps to get some light on this process.”

News of the botched execution prompted a storm of criticism. Many blamed recalcitrant Oklahoma officials for pursuing an experimental and secretive lethal injection method, and some blamed the U.S. Supreme Court for refusing to weigh in on similar execution secrecy cases in other states.

“This is one of the worst botches that we’ve had,” said Denno, the Fordham law professor. “All of this was predictable and foreseeable. How many times does this have to take place? … We have all the evidence we need to show this is a highly problematic and potentially unconstitutional procedure.”

The American Civil Liberties Union of Oklahoma likened the execution process to “hastily thrown-together human science experiments” and called for a moratorium.

A spokesman for Oklahoma Attorney General E. Scott Pruitt issued a terse statement: “We are gathering information on what happened tonight in order to evaluate.”

Texas, the state that performs the most executions, said the Oklahoma incident would not prompt any changes there. “Texas does not use the same drugs,” a Department of Corrections spokesman said. “We use a single lethal dose of pentobarbital and we have done so since 2012.”

The Oklahoma incident could eventually force the U.S. Supreme Court to reconsider whether the death penalty constitutes cruel and unusual punishment, which is barred by the U.S. Constitution.

Six years ago, the Supreme Court rejected a cruel and unusual punishment challenge to lethal injections in a Kentucky case. Attorneys argued that prison officials could not be trusted to administer the three drugs in a way that would ensure that a prisoner was put to death without suffering great pain.

The Supreme Court ruled that states could proceed with lethal injections as long as they developed good and safe procedures to administer the drugs. But the court left the door open to future challenges.

The Oklahoma case is sure to be cited as evidence that state prison authorities cannot be trusted to capably administer lethal injections.

Erwin Chemerinsky, dean of the University of California, Irvine School of Law, said as much in a statement Tuesday night: “For the state to inflict such great suffering is the very definition of cruel and unusual punishment. Courts must step in and prevent executions with such untested protocols that have the potential for inflicting such terrible suffering.”

Photo: Ken Piorkowski via Flickr