A man who murdered a sheriff's deputy years after doctors removed part of his brain will be put to death in Missouri next week - but his lawyers are fighting for him to be saved. Cecil Clayton, from Purdy, will be executed at the state prison in Bonne Terre at 6pm on March 17 for the November 1996 shooting of Barry County Sheriff's Deputy Christopher Castetter. But his attorneys are making a last-ditch attempt to save him by calling for a competency trial - saying a traumatic brain injury makes it impossible for him to understand his death sentence. In 1972, 24 years before he killed the officer, Clayton was using a sawmill when a board splintered and a shard went into his head above his right eye, the St Louis Post-Dispatch reported. Facing death: Cecil Clayton is scheduled to die in Missouri next week but his lawyers are calling for a competency hearing. Twenty years before he murdered a cop, he had part of his brain removed, they say . Doctors were forced to remove 20 per cent of his frontal lobe, the area of the brain that controls decision making and emotions, the newspaper reported as it called for Clayton to be spared. Following the accident and before the arrest, Clayton frequently went to mental health facilities, spending up to 15 months at a time under psychiatric care. Then the evening before Thanksgiving in 1996, Deputy Castetter responded to a call about a suspicious vehicle parked outside Clayton's girlfriend's mother's home. Earlier that night, Clayton and his girlfriend had been arguing, and prosecutors said he then took a loaded gun to her mother's house. Clayton walked up to the deputy's patrol car window and shot him in the head at point-blank range. Castetter, a 29-year-old married father-of-three, died in the hospital later that day. He was convicted of the murder in October 1997 and sentenced to death later that year. His attorneys argued that he was mentally incompetent to stand trial but despite their appeals, state and federal appeals courts have upheld the conviction and the death penalty. His lawyers are now seeking a competency hearing to determine whether he understands his death penalty. Mental health professionals who have examined him agree that he is mentally impaired and has mental health issues, including dementia. Killed: Barry County Sheriff's Deputy Christopher Castetter, pictured left, was shot dead by Clayton, pictured right in an old mug shot, as he responded to a call about a suspicious vehicle in 1996 . His most recent IQ test found he had an IQ of just 71 - 29 points below the average. 'He is not simply incompetent legally; he would be unable to care for himself or manage basic self-care, were he not in a structured environment that takes care of him,' according to a doctor who examined him, the Kansas City Star reported. 'He can shower, groom, eat, walk; it is his comprehension, judgment, memory, limited intelligence and social deficits that plague him.' But there is no agreement on how much he understands his death penalty or his other options. 'If you can prove mental retardation, you can get exempted, but mental illness alone is not an exemption to the death penalty,' Richard Dieter, executive director of the Death Penalty Information Center, told the New York Times. In Missouri, the director of the Department of Corrections is the only one with the authority to order a competency hearing, and last year, he called on a doctor to examine Clayton. Dr. James Reynolds of the Missouri Department of Mental Health concluded that Clayton is mentally ill, but could not be certain that he doesn't understand his death sentence. Execution: He is scheduled to be put to death at the state prison in Bonne Terre, pictured, next Tuesday . Death: His family and lawyers are arguing that he is child-like and does not understand the significance of his death penalty. They are calling for his execution at Bonne Terre (pictured) to be stopped . But Clayton's lawyers say, while he may have conversations in which he understands he is about to be executed, he will later forget that conversation ever happened. His family have also called for a fair hearing on the issue. 'He is brain-damaged, and talking with him is like talking to a child,' Clayton's daughter, Jena Clayton, said during his clemency petition, the Kansas City Star reported. 'I do not believe we are the kind of country that executes the disabled.' Clayton, who is the state's oldest death row inmate, will be put to death between 6pm on March 17 and 5.59pm on March 18. He will become the second person put to death in the state in 2015, after a record 10 executions in Missouri in 2014. Last month, Walter Storey was put to death for slitting his neighbor's throat 25 years ago.
Lawyers for Cecil Clayton are seeking a competency trial to halt his execution, which is scheduled for March 17 at 6pm . In 1972, 24 years before he shot dead a police officer, he suffered a sawmill accident that caused a shard of wood to go into his head . Doctors were forced to remove 20 per cent of his frontal lobe . His lawyers argue that he has a low IQ, mental illness and is not competent enough to understand his death sentence . But a doctor from Missouri Department of Mental Health previously concluded that he did understand the punishment .