OKLAHOMA CITY — Gov. Mary Fallin agreed Thursday that all executions in Oklahoma should be delayed after an autopsy report revealed that the wrong drug was used to stop an inmate’s heart in January — one that experts say doesn’t work as quickly or effectively. 

Fallin said “it became apparent” last week that prison officials used potassium acetate — not potassium chloride, as required under the state’s protocol — to execute Charles Frederick Warner in January.

“Until we have complete confidence in the system, we will delay any further executions,” Fallin said in a statement.

The autopsy report, prepared the day after Warner’s Jan. 15 execution and revealed by The Oklahoman newspaper on Thursday, describes the instruments of death in detail. It says the Office of the Chief Medical Examiner received two syringes labeled “potassium chloride,” but that the vials used to fill the syringes were labeled “single dose Potassium Acetate Injection.”

That contradicts the official execution log, initialed by a prison staffer, which says the state properly used potassium chloride to stop his heart, according to a copy obtained by The Associated Press.

“We cannot trust Oklahoma to get it right or tell the truth,” said Dale Baich, an attorney representing Oklahoma death row inmates. “We will explore this in detail through the discovery process in the federal litigation.”

Fallin declined to say if she still has confidence in prisons director Robert Patton. She said she would wait until Attorney General Scott Pruitt completes an investigation into both Warner’s execution and last week’s mix-up.

“I want to let the attorney general do his job first, tell us what’s factual and what’s not, give us the information, and then we’ll make a judgment then,” Fallin told the AP.

Patton oversaw both Warner’s execution and the April 2014 lethal injection of Clayton Lockett, who writhed on the gurney, moaned and pulled up from his restraints. Execution team members considered trying to save his life and even taking Lockett to an emergency room before he finally died, 43 minutes after his initial injection.

Warner had been scheduled to die the same night, but his death was delayed for months after Lockett’s execution went awry.

The next inmate scheduled to die, Richard Glossip, came within hours of his lethal injections last week before prison officials informed the governor that they had received potassium acetate instead of potassium chloride from a pharmacist, whose identity is shielded by state law.

That discovery prompted new questions about past executions, including Warner’s.

Potassium chloride, which stops the heart, is the final drug in the state’s three-drug protocol, following the application of a sedative, midazolam; and a paralytic, rocuronium bromide, which prevents normal breathing.

Patton said last week that prison authorities discovered the error as they prepared for Glossip’s execution and immediately contacted the supplier, “whose professional opinion was that potassium acetate is medically interchangeable with potassium chloride at the same quantity.”

But experts on pharmaceuticals and chemistry told the AP on Thursday that differences between the two forms could be relevant.

Potassium chloride is more quickly absorbed by the body, in part because its pH level is considerably lower than blood. Potassium acetate takes longer and more of it would be needed to achieve the same effect, said Dr. Mohamed Jollah, who teaches at Creighton University’s Center for Drug Information and Evidence Based Practice in Omaha, Nebraska.

Given the number of empty vials described in Warner’s autopsy report, it suggests he received 240 milliequivalents of potassium — the same as the protocol. But because it was an acetate, this amount might not have worked as quickly as a chloride, experts say.

Robert Bachman, a chemistry professor at The University of the South in Sewanee, Tennessee, told the AP that failing to adjust the dosage to account for the difference between chloride and acetate could make the potassium less effective.

In Warner’s case, after the midazolam was administered, he complained that “my body is on fire.” But he showed no other obvious signs of distress, and was declared dead 18 minutes after his execution began.

The point of the three-drug protocol is to provoke a quick, humane death by making the inmate unconscious before the lungs and heart stop. But attorneys for the inmates maintain that midazolam is not a proper drug to completely render them incapable of feeling pain.

The switch from potassium chloride could open the door to other legal challenges: Last week, before Warner’s autopsy report revealed otherwise, the Death Penalty Information Center said potassium acetate had never been used in a U.S. execution.

Fallin said she was not told that the wrong drug may have been used to execute Warner until last week.

“I was not aware, nor was anyone in my office aware, of that possibility until the day of Richard Glossip’s scheduled execution,” she said. “It is imperative that the attorney general obtain the information he needs to make sure justice is served competently and fairly.”