(CNN) -- A federal appeals court lifted the stay of execution for white supremacist serial killer Joseph Paul Franklin early Wednesday morning -- moving the man blamed for 22 killings and the shooting of Hustler magazine publisher Larry Flynt closer to death.
The next step for Franklin's attorneys would be to appeal the case to the U.S. Supreme Court. It was not clear early Wednesday when, or if, they plan to do so.
Watch: CNN's interview with Franklin days before his scheduled execution
Franklin is on death row for the 1977 murder of Gerald Gordon outside a synagogue in St. Louis. He's been blamed for a total of 22 killings between 1977 and 1980 in a bid to start a race war.
He is challenging Missouri's decision to use the drug pentobarbital in its lethal injection protocol, arguing it would violate the Constitution's ban on cruel and unusual punishment.
The 8th U.S. Circuit Court of Appeals decided early Wednesday that Franklin's lawyers had not provided enough evidence to warrant a stay of execution.
This decision came after a number of a legal maneuvers in the last couple days.
On Tuesday, U.S. District Judge Nanette Laughrey granted a stay of execution, finding Franklin's lawyers showed the use of pentobarbital carried "a high risk of contamination and prolonged, unnecessary pain beyond that which is required to achieve death."
"Given the irreversible nature of the death penalty and plaintiffs' medical evidence and allegations, a stay is necessary to ensure that the defendants' last act against Franklin is not permanent, irremediable cruel and unusual punishment in violation of the Eighth Amendment," Laughrey wrote.
Another federal judge granted a second stay Tuesday, based on a separate defense petition contesting Franklin's competency.
"The Court concludes that a stay of execution is required to permit a meaningful review," U.S. District Judge Carol Jackson wrote.
The state appealed both stays to the 8th U.S. Circuit Court of Appeals.
That ruling came early Wednesday morning.
The execution warrant window is 24 hours, meaning that if nothing changes, Franklin could still be put to death sometime Wednesday.
Franklin had been scheduled to be executed in the state prison in Bonne Terre, Missouri, about 60 miles south of St. Louis. But Missouri and other states that conduct executions have had to scramble for new drugs after European-based manufacturers banned American prisons from using their drugs in executions.
Missouri had planned to use propofol, the surgical anaesthetic made infamous by the death of pop star Michael Jackson. But Gov. Jay Nixon reversed that decision after being warned the European Union -- whose members forbid capital punishment -- might halt shipments of the drug, leading to shortages for medical purposes.
In October, the state announced it would use pentobarbital, which would be provided by an unnamed compounding pharmacy. Franklin's lawyers argued that would raise the risk of contamination and a painful death.
Nixon denied clemency for Franklin on Monday, arguing Franklin had committed "merciless acts of violence, fueled by hate."
In addition to the killings, Franklin admitted to the attempted assassinations of Hustler magazine publisher Larry Flynt in 1978 and civil rights leader Vernon Jordan in 1980. Flynt, who was paralyzed by Franklin's bullet, has called for clemency for Franklin, saying "the government has no business at all being in the business of killing people."