OKLAHOMA CITY (AP) - Jurors and others in Judge Donald Thompson's courtroom kept hearing a strange whooshing noise, like a bicycle pump or maybe a blood pressure cuff. During one trial, Thompson seemed so distracted some jurors thought he was playing a hand-held video game or tying fly-fishing lures behind the bench. The explanation, investigators said, is even stranger than some imagined: the judge had a habit of masturbating with a penis pump under his robe during trials.

The lurid allegations have led to criminal charges against Thompson, brought an embarrassing end to a solid career and shocked many of his colleagues. The case could also lead to a wave of appeals from defendants claiming the judge was not paying attention while presiding over their cases.

Thompson, a 58-year-old married father of three grown children, has denied the allegations and said the pump was just a gag gift received from a hunting buddy on his 50th birthday. He retired in August after being threatened with removal from the bench but still faces indecent-exposure charges brought against him last month.

"We're certainly saddened by the thought that the prosecutor filed charges," said Clark Brewster, Thompson's lawyer.

"We thought all this was dealt with when he resigned. We didn't feel like anything that was alleged rose to the level of criminal charges."

The trials during which he allegedly used the pump included murder cases, as well as a libel suit in which a jury ordered the company that publishes the Oklahoman newspaper, a website and a TV station to pay $3.7 million.

Oklahoma Attorney General Drew Edmondson, who filed the paperwork to remove Thompson from the bench, said he would be surprised if the scandal did not lead to appeals. But he said: "I don't know if they will be successful. They will still have to show actual prejudice to the point that something was done in error."

Jim Wall, police chief in the small town Sapulpa, said he had heard rumours of the judge's behind-the-bench activities for about a month but added: "You've got the most powerful man in Creek County and I think a lot people were intimidated by him."

Police built a case against the judge after one of Wall's officers testified during a 2003 murder trial. From the witness stand, the officer saw a piece of plastic tubing disappear under Thompson's robe. During a lunch break, officers took photographs of the pump under the desk.

Investigators later collected carpet samples, Thompson's robes and the chair from behind the bench and found semen, court records showed.

A former state legislator and a judge with more than 20 years on the bench in Creek County in eastern Oklahoma, Thompson was well-liked in the community and had helped many young prosecutors and judges learn their jobs. But those who know him said he had become withdrawn in the last few years.

Thompson's court reporter, Lisa Foster, told authorities she saw him use the pump at least 10 times during trials. She said the first time in court was in 2000 but she did not tell authorities.

"I didn't want to be found dead in a ditch somewhere," she said.

Foster told authorities she saw Thompson use the device almost daily during the August 2003 murder trial of Kevin Vomberg, a man accused of shaking a toddler to death. The case ended in a hung jury. The whooshing sound could be heard on Foster's audiotape of the trial.

When jurors at the trial asked the judge about the sound, Thompson said he hadn't heard it but would listen for it.

Foster and a bailiff were fired by Thompson after giving statements against him.

"I always thought he was an excellent trial judge," said Don Nelson, who tried more than 40 cases before Thompson as the prosecutor assigned to his court.

Nelson handled a murder trial during which authorities said Thompson used the pump. The jury ended up convicting the defendant on the lesser charge of manslaughter.

"I never heard anything that was going on," Nelson said.

"I was completely shocked and couldn't believe it."