A federal judge has overturned the capital murder conviction of a Houston man who fatally shot a motorcycle officer, saying the state trial judge had a "deep-seated and vocal bias" against the defendant.

U.S. District Judge Kenneth Hoyt issued an opinion late Friday overturning the conviction of Carl Wayne Buntion, convicted in 1991 of killing officer James Irby during a traffic stop.

Hoyt said in his 61-page opinion that state District Judge Bill Harmon deprived Buntion of his constitutional right to a fair trial by bullying his lawyers, meeting privately with prosecutors and deferring to their wishes, and making remarks in court such as he was "doing God's work" by seeing that Buntion was executed.

Harmon placed a Judge Roy Bean postcard on the bench during jury selection, giving the impression that he was a "hangin' judge," Hoyt said.

Even before hearing evidence, Hoyt wrote, "Judge Harmon decided that Buntion was guilty and should die."

Buntion was a passenger in a car stopped for a minor traffic violation by Irby while he was on motorcycle patrol June 27, 1990.

Buntion got out of the car and shot Irby in the forehead with a .357-caliber Magnum that shredded half of Irby's brain.

"Mr. Buntion has never disputed the fact that he shot and killed officer Irby that day," said Dick Wheelan of Houston, who has represented Buntion for at least eight years of the appeal process.

"Since the beginning he has maintained that he was acting in self defense," Wheelan said.

Jerry Strickland, spokesman for the Texas Attorney General's Office, which represents the state in all federal cases, said the office had contacted the Harris County District Attorney's Office and Irby's family and were reviewing the decision.

Strickland said his office had 30 days to decide whether to appeal to the 5th U.S. Circuit Court of Appeals.

The state must retry or release him within 180 days if there is no appeal.

harvey.rice@chron.com