Marvin Wilson, 54, was pronounced dead at 6:27 p.m., 14 minutes after his lethal injection began at the state prison in Huntsville. Wilson's attorneys had argued that he should have been ineligible for capital punishment because of his low IQ.

In their appeal to the high court, his attorneys pointed to a psychological test conducted in 2004 that pegged Wilson's IQ at 61, below the generally accepted minimum competency standard of 70.

But lower courts agreed with state attorneys, who argued that Wilson's claim was based on a single test that may have been faulty and that his mental impairment claim isn't supported by other tests and assessments of him over the years.

The Supreme Court denied his request for a stay of execution less than two hours before his lethal injection began. Lead defense attorney Lee Kovarsky said he was "gravely disappointed and saddened" by the ruling, calling it "outrageous that the state of Texas continues to utilize unscientific guidelines ... to determine which citizens with intellectual disability are exempt from execution."

Wilson was convicted of murdering 21-year-old Jerry Williams in November 1992, several days after police seized 24 grams of cocaine from Wilson's apartment and arrested him. Witnesses testified that Wilson and another man, Andrew Lewis, beat Williams outside of a convenience store in Beaumont, about 80 miles east of Houston. Wilson, who was free on bond, accused Williams of snitching on him about the drugs, they said.

Witnesses said Wilson and Lewis then abducted Williams, and neighborhood residents said they heard a gunshot a short time later. Williams was found dead on the side of a road the next day, wearing only socks, severely beaten and shot in the head and neck at close range.

Wilson was arrested the next day when he reported to his parole officer on a robbery conviction for which he served less than four years of a 20-year prison sentence. It was the second time he had been sent to prison for robbery.

At Wilson's capital murder trial, Lewis' wife testified that Wilson confessed to the killing in front of her, her husband and his own wife.

"Don't be mad at Andrew because Andrew did not do it," Lewis' wife said Wilson told them. "I did it."

Lewis received a life prison term for his involvement.

Wilson was the seventh person executed by lethal injection in Texas this year. At least nine other prisoners in the nation's most active death penalty state have execution dates in the coming months, including one later this month.