An attorney for condemned killer Allen Nicklasson is asking the Missouri Supreme Court for a stay of execution, citing concerns about Missouri's planned use of the anesthetic propofol for the first time as a lethal injection drug.

Attorney Jennifer Herndon filed the motion on Wednesday. It wasn't clear when the court would issue a ruling.

The Missouri Department of Corrections has expressed confidence in propofol as an execution drug, but Herndon raised concerns that it could cause Nicklasson to suffer.

Nicklasson was convicted of the 1994 killing of Excelsior Springs businessman Richard Drummond, who stopped to help when a car used by Nicklasson and two others broke down on Interstate 70. Nicklasson was determined to be the shooter. Another man in the car, Dennis Skillicorn, was executed in 2009. The third, Tim DeGraffenreid of Blue Springs, was a teenage acquaintance they brought along with them. He eventually led authorities to Drummond’s body in a Lafayette County field. He received a life sentence.

Also on Wednesday, the Missouri Department of Corrections said that it will return a shipment of propofol, nearly a year after the drug distributer's urgent request for it to be sent back.

The department said in a news release that it still has a supply of propofol, but it didn't clarify whether it had enough of the drug for the scheduled executions of Nicklasson and Joseph Franklin. Phone and email messages left with the agency's spokespeople were not returned.

The announcement came a day after the department released documents to the American Civil Liberties Union, in response to an open records request, that included a Nov. 2 email sent by Dale Kelley, an executive with Louisiana-based pharmaceutical distributor Morris & Dickson Co., to Department of Corrections Director George Lombardi.

The email said a "system failure" led Morris & Dickson to send propofol to the department in violation of the company's agreement with the drug's manufacturer, Germany-based Fresenius Kabi. The email said that because of the mistake, Morris & Dickson was suspended from distributing propofol, which is by far the most popular anesthetic used at U.S. hospitals and clinics.

The drug has never been used in an execution, and Missouri's plan to use it has prompted the anti-death penalty European Union to say it could limit the drug's export. Nearly 90 percent of the U.S. supply comes from Europe.

"Please — Please — Please HELP ... this system failure — a mistake — 1 carton of 20 vials — is going to affect thousands of Americans," Kelley wrote.

Phone messages left with Morris & Dickson were not returned.

The Corrections Department said its remaining supply of propofol was produced by a domestic manufacturer.

The executions would be the first in Missouri since the state dropped its three-drug execution method in favor of propofol in April 2012. The switch was made after the state couldn't obtain its previously used drugs because makers began prohibiting their use in executions.

The change to propofol — the drug used in pop star Michael Jackson's overdose death in 2009 — also spurred a lawsuit filed on behalf of nearly two dozen death-row inmates. The suit argues the drug could result in pain and suffering for the condemned.

The case was scheduled to go to trial this week, but court records show a 30-day delay was granted because of changes the state made on Sept. 24 to its execution protocol, such as changing the amount of propofol that would be placed in syringes. That means the case won't go to trial until after Nicklasson's scheduled execution.