HOUSTON (AP) A Dallas man condemned for a shooting spree that left five people dead during a robbery at a suburban Dallas car wash has lost a federal court appeal, moving him a step closer to execution.

Robert Wayne Harris was convicted of two of the five slayings at the Mi-T-Fine Car Wash in Irving in March 2000. He had been fired from his job there a few days earlier for exposing himself to a female customer.

Attorneys for Harris told the 5th U.S. Circuit Court of Appeals in New Orleans he was mentally impaired, making him ineligible for execution under Supreme Court guidelines. The appeals court said there was no evidence to support his claim.

"Harris has offered no expert opinion that he is mentally retarded and no IQ score at 70 or below from a test taken prior to age 18," a three-judge panel of the court wrote in a ruling posted late Monday.

Harris, 40, does not yet have an execution date.

His lawyer, Lydia Brandt, said Tuesday she would take the appeal to the Supreme Court.

A Dallas County jury deliberated 11 minutes in September 2000 before finding Harris guilty of killing Rhoda Wheeler, 46, and Agustin Villasenor, 36. The same jury decided three days later Harris should die.

Harris also was charged with capital murder but not tried for the slayings of the three others shot in the same attack.

A sixth employee at the car wash survived a gunshot wound to the head and testified how Harris forced him and two co-workers to kneel at gunpoint before they were shot with a semiautomatic handgun.

Another worker testified he walked in on the scene as Harris was standing over the bodies of three victims. Harris told him there were three other bodies elsewhere. Harris then showed up at a store nearby where the frantic worker was calling 911 to report the carnage. Harris joined in the call and told the dispatcher he had gone to the car wash to talk to his manager after losing his job and discovered the bloody scene.

Harris was arrested the next day, hiding at a former girlfriend's house. The following day, he led police to the decomposing body of a woman who had been missing about four months.

During the punishment phase of his trial, prosecutors presented evidence showing Harris at age 15 was placed in a state school after attacking an aunt with a hammer. As an adult, he had three burglary convictions and spent most of his seven years in prison in administrative segregation, the Texas prison system's most restrictive custody. The car wash shootings occurred about nine months after he was released.

Prison records and testimony at his trial showed he repeatedly threatened officers, set fire to his cell and threatened and fought with other inmates. A defense psychiatrist described him as anti-social and suffering from depression compounded by a low IQ.