By Mary Wisniewski
(Reuters) - Missouri on Tuesday plans to execute a man who murdered three people in the robbery of a convenience store in 1994.
Ernest Lee Johnson, 55, is scheduled to die by lethal injection at around 6 p.m. at the state prison in Bonne Terre, Missouri, unless granted clemency by the state's governor or the U.S. Supreme Court agrees to hear his case.
Johnson was convicted of bludgeoning to death Mary Bratcher, Mabel Scrubbs and Fred Jones using a hammer, a screw driver and a gun, according to court records. Defense attorneys have argued in unsuccessful appeals that he is mentally retarded and not eligible for execution.
Defense attorneys have filed a petition to appeal to the U.S. Supreme Court, arguing that because of Johnson's slow-growing brain tumor, the pentobarbital used in lethal executions in Missouri could cause him to suffer seizures and pain, according to the Columbia Tribune.
Defense attorney Jeremy Weis said in an interview with Reuters that a 2008 surgery to remove Johnson's slow-growing tumor did not get all of it, and that he has had prior seizures. Weis said that a portion of Johnson's brain is missing.
The Missouri Supreme Court on Monday turned down Johnson's request that it appoint a judge to consider evidence that he is intellectually disabled and it would be unconstitutional to execute him, the Columbia Tribune said.
Missouri Governor Jay Nixon has received and is reviewing Johnson's petition for clemency, spokesman Scott Holste said on Monday.
On Oct. 2, Nixon, a Democrat, commuted the sentence of the last man scheduled to die in Missouri, Kimber Edwards, to life in prison.
A total of 25 people have been executed in the United States so far this year, according to the Death Penalty Information Center, including six in Missouri.
(Reporting by Mary Wisniewski in Chicago; Editing by Sandra Maler)