BONNE TERRE, Mo. (CN) - Missouri's oldest Death Row inmate, who was missing part of his brain, was executed Tuesday.
Cecil Clayton, 74, was pronounced dead at 9:21 p.m., eight minutes after the execution started.
Clayton's last-minute appeal to the U.S. Supreme Court was denied Tuesday afternoon and Gov. Jay Nixon denied clemency.
Clayton's attorneys argued that he lacked the mental competency to be executed because of neurological issues. Clayton had dementia and a 1972 sawmill accident forced surgeons to remove 20 percent of the frontal lobe of his brain.
Clayton was convicted of gunning down Barry County Sheriff's Deputy Christopher Castetter in 1996. Castetter was murdered while investigating a report of a suspicious vehicle.
"As one who has carried a badge most of my adult life, I share the outrage of every Missourian at the murder of law enforcement officer Deputy Christopher Castetter," Missouri Attorney General Chris Koster said in a statement. "Cecil Clayton tonight has paid the ultimate price for his terrible crime."
On Saturday, a split Missouri Supreme Court declined to intervene, in a 4-3 decision.
In a 47-page opinion , Judge Paul C. Wilson wrote that Clayton failed to make the threshold showing to justify a stay.
"The Court has reviewed the remaining evidence submitted in support of Clayton's petition, nearly all of which was reviewed by, described, and relied upon by one or more of Clayton's three experts. ... This evidence confirms the facts the experts describe, i.e., that Clayton continues to suffer effects from his 1972 brain injury but Clayton also understands that he was convicted of murdering Deputy Castetter and that he is to be executed for that crime," Wilson wrote.
Chief Judge Mary Russell and Judges Patricia Breckenridge and Zel Fischer concurred.
Judge Laura Denvir Stith wrote in dissent that Clayton was entitled to a hearing for his mental competency and to determine whether he understands the circumstances surrounding his execution.
"The majority simply ignores the requirement that, unless Mr. Clayton understands the rationale for his execution and matters 'in extenuation, arguments for executive clemency or reasons why the sentence should not be carried out,' then he is not competent to be executed," Stith wrote. "But shutting its eyes to this requirement does not make it go away."
Judge George W. Draper III and Richard B. Teitelman concurred with Stith.