NEW ORLEANS (AP/CBSDFW.COM) — A Dallas man condemned for a shooting spree that left five people dead during a robbery at a car wash has lost a federal court appeal.

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

Attorneys for the 40-year-old Harris told the 5th U.S. Circuit Court of Appeals in New Orleans that he was mentally impaired, making him ineligible for execution under Supreme Court guidelines. The appeals court ruling, which was posted late Monday, says there’s no evidence to support his claim.

At the time of the murders, Harris had a prior prison record for burglary.

Harris does not yet have an execution date.

(Copyright 2012 by CBS Local. The Associated Press contributed to this report.  All Rights Reserved.)