ST. LOUIS (AP) — The execution of a Missouri man was in limbo Wednesday following the U.S. Supreme Court’s decision to halt the lethal injection shortly before it was set to take place.

Ernest Lee Johnson, convicted of beating three people to death with a claw hammer, was scheduled to die at 6 p.m. Tuesday at the Missouri state prison in Bonne Terre.

But in a last-minute decision, the Supreme Court sent the case back to the 8th U.S. Circuit Court of Appeals to consider whether it properly dismissed a complaint from Johnson that alleged execution drugs could trigger painful seizures because of his brain tumor.

Johnson, 55, argues that the execution drug Missouri uses could cause seizures because he still has part of a benign brain tumor, and surgery to remove the rest of it in 2008 forced the removal of up to 20 percent of his brain tissue. His attorneys said Johnson has had a low IQ since elementary school.

The appeals court had taken no action by mid-morning. State law allows prison officials 24 hours to carry out an execution, meaning the deadline in Johnson’s case is 6 p.m. Wednesday.

Johnson’s attorney, Jeremy Weis, said Wednesday that it appeared unlikely the dispute would be settled by the deadline. On Tuesday night, Department of Corrections spokesman Mike O’Connell said there was “no indication of any kind” the issue would be resolved Wednesday.

Weis said Johnson understood just enough of what was happening to know his life was spared, at least for now.

“I can’t say he understood the issue. He understands that he got a stay and they won’t take him out and kill him,” Weis said.

A second appeal also is pending, to the Missouri Supreme Court, claims Johnson’s life should be spared because of the mental disability. The Missouri Attorney General’s Office has said both appeals are without merit.

Messages seeking comment from the attorney general’s office on Wednesday were not returned.

Johnson was convicted of three counts of first-degree murder for killing three people — 46-year-old Mary Bratcher, 57-year-old Mable Scruggs and 58-year-old Fred Jones — during a closing-time robbery of a Casey’s General Store in Columbia on Feb. 12, 1994.

All three workers were beaten to death with a claw hammer. Bratcher was also stabbed at least 10 times with a screwdriver, and Jones was shot in the face.

Johnson wanted money to buy drugs, authorities said. He was arrested after police found a bank bag, stolen money and store receipts at Johnson’s house.

Johnson grew up in a troubled home. Weis, his attorney, said Johnson’s IQ was measured at 63 while still in elementary school. Testing after his conviction measured the IQ at 67, still a level considered mentally disabled.

He was already on death row in 2001 when the U.S. Supreme Court ruled that executing mentally disabled inmates was unconstitutionally cruel. A new sentencing hearing was ordered, but Johnson was again sentenced to death in 2003.

The Missouri Supreme Court tossed that sentence, too, but Johnson was sentenced to death for a third time in 2006.

Doctors couldn’t remove his entire brain tumor in 2008. Weis said the combination of the remaining tumor and the fact that Johnson lost about one-fifth of his brain has left him prone to seizures. He also has difficulty walking.

Missouri’s execution drug is a form of pentobarbital, but the state won’t say where it got the drug. According to a court filing, Dr. Joel Zivot examined MRI images of Johnson’s brain.

Zivot wrote in his report that Johnson faces “a significant medical risk for a serious seizure as the direct result of the combination of the Missouri lethal injection protocol and Mr. Johnson’s permanent and disabling neurologic disease.”

Court filings by the Attorney General’s office note that Missouri has carried out 18 “rapid and painless” executions since it went to the one-drug method in November 2013.

Other death row inmates have had mixed success in pursuing claims that medical conditions should preclude them from execution.

In May 2014, the U.S. Supreme Court stopped the execution of Missouri inmate Russell Bucklew, who claimed the execution drug could cause suffering due to a rare congenital condition that causes weakened and malformed blood vessels, as well as tumors in his nose and throat. The case remains unresolved.

In March, Cecil Clayton claimed a sawmill accident that damaged his brain in the 1970s should prohibit execution. The courts disagreed, and Clayton, 74, was executed.