Marvin Wilson (Texas prison photo)

HUNTSVILLE (August 7, 2012)--Convicted killer Marvin Wilson, 54, was executed Tuesday in Huntsville for the abduction and shooting death of a police informant in 1992 in Beaumont.

The U.S. Supreme Court cleared the way for his execution Tuesday afternoon, rejecting his final appeal.

His attorneys argued that he was mentally impaired and should have been spared from lethal injection.

A test in 2004 showed his IQ to be 61, below the generally accepted competency standard of 70.

The Supreme Court has barred execution of mentally impaired people.

But state lawyers contended the single test that indicated mental impairment was faulty and said the results from all other psychological testing of the Jefferson County man were different.

The state’s Catholic bishops sent a letter to Gov. Rick Perry and the Board of Pardons and Paroles citing the results of the 2004 psychological test and asking them to block the execution.

"We stand in solidarity with victims and their loved ones, however, when it comes to matters of life and death, morality and common sense call for justice, mercy, and for careful safeguards," the letter said.

Wilson's lead attorney, University of Maryland law professor Lee Kovarsky, said earlier Tuesday if Texas proceeded with the execution, Wilson would be the lowest-IQ Texas prisoner put to death despite the Supreme Court ruling that banned the execution of mentally impaired inmates.

Wilson was sentenced to die for the Nov. 9, 1992 abduction and murder of police informant Jerry Williams, 21, who prosecutors say was killed because he was the source of a tip that led to a search of Wilson’s apartment five days earlier that turned up more than 24 grams of cocaine and led to Wilson’s arrest.

Wilson was released on bond after the arrest and threatened to get the “snitch” responsible for his arrest, court documents show.

Several people witnessed Williams’ abduction from the parking lot of a Beaumont grocery store and testified that they saw Wilson beat Williams.

They testified that Wilson asked him, “What do you want to be a snitch for? Do you know what we do to a snitch? Do you want to die right here?”

Witnesses testified that Williams begged for his life and then ran across the street to a field where Wilson caught him while his co-defendant, Andrew Lewis, 56, drove a car to the field.

Then Lewis and Wilson forced Williams into the car and drove toward the Mobil refinery in Beaumont.

Two of the witnesses testified they later heard gunshots from the direction of a refinery

Williams was found dead the next day, lying on the side of a road wearing only socks.

He had been severely beaten and then shot at close range in the head and neck.

Lewis, who testified against Wilson, received a life sentence.