Marvin Wilson (Texas prison photo)

HUNTSVILLE (August 6, 2012)--Attorneys for convicted killer Marvin Wilson, 54, who faces execution Tuesday in Huntsville, want the U.S. Supreme Court to stop the punishment.

They’re asking the high court to reverse rulings from other courts that have refused to halt the execution despite a psychological test that set Wilson's IQ at 61.

That's a score they insist indicates mental impairment and makes Wilson ineligible for execution Tuesday evening in Huntsville for killing a police informant in Beaumont 20 years ago.

State lawyers argue the result from a 2004 test is faulty and that all other tests showed his IQ above the impairment threshold of 70.

Wilson was sentenced to die for the shooting death of Jerry Williams, 21, who had provided information that led to Wilson's drug arrest a week earlier in 1992.

Wilson was accused of abducting Williams and then shooting him to death during a confrontation.