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. Another man in the car, Dennis Skillicorn, was executed in 2009.