An attorney for a Missouri inmate scheduled to die this week is seeking to halt the execution over concerns about the secretive process of obtaining and using lethal injection drugs.

Walter Timothy Storey is scheduled to die at 12:01 a.m. Wednesday for killing a neighbor in St. Charles in 1990. After a state-record 10 executions in 2014, Storey would be the first person put to death this year in Missouri.

Attorney Jennifer Herndon says Missouri's secretive process of purchasing lethal injection drugs from an unnamed compounding pharmacy creates the risk that Storey could suffer a painful death.

The 8th U.S. Circuit Court of Appeals has already turned down the stay request. Herndon has appealed to the Missouri Supreme Court and plans an appeal to the U.S. Supreme Court.