At 6:27 p.m. local time on Tuesday, Aug. 7, Texas executed Marvin Lee Wilson, a 54-year-old man who was found guilty of a 1992 murder in Beaumont, Texas. Wilson was on the state’s death row for 20 years, but his lawyers and human-rights activists argued that the Lone Star State was going to kill a mentally retarded man in violation of the Supreme Court and the U.S. Constitution. The Supreme Court denied a stay of the execution Tuesday.

In 2002 the Supreme Court ruled in Atkins v. Virginia that the execution of mentally retarded individuals is strictly prohibited. However, the court left the precise definition of mental retardation to the states, noting that legal criteria “generally conform” to clinical definitions issued by the American Association on Mental Retardation and the American Psychiatric Association.

Wilson, who was subjected to a battery of psychological tests, was found to fit those criteria. Prosecutors did not present any scientific evidence to contradict the finding that Wilson was mildly mentally retarded, but argued nevertheless that he was competent to be executed under application of the Briseño factors—a test that considers whether, for instance, a person can exhibit leadership and whether he can lie in his self-interest. (In that case, the court used the example of Lennie, the character in John Steinbeck’s novel Of Mice and Men, to demonstrate someone who would be considered by most to be mentally retarded.)

Texas courts and the U.S. Fifth Circuit Court of Appeals agreed with the state.

The Daily Beast has annotated the report of the neuropsychologist, Donald Trahan, which is at the center of Wilson’s petition to the Supreme Court. Trahan wrote the report following his 8-hour assessment of Wilson in 2004. We spoke to both Trahan and Richard Dieter, the executive director of the Death Penalty Information Center.