Documents filed in U.S. District Court in Martinsburg show that the evidence includes testimony Jefferson County Sheriff Robert Shirley gave during a 2004 sentencing hearing in an unrelated case. A transcript reveals Shirley admitted firing a gun while on duty during a personal dispute with another man.

That transcript, which shows the shooting never resulted in criminal charges or prosecution, "is evidence of defendant's readiness to abuse the power of his position,'' Assistant U.S. Attorney Paul Camilletti wrote in a notice filed with the court last week.

Shirley's attorney, Kevin Mills, said he is reviewing the government's motion and will respond with his own.

Besides ignoring Shirley's "long history of dedicated community service, putting his life on the line,'' Mills said, the filing could compromise his client's right to a fair trial.

"We believe it relates to inadmissible evidence that is alleged to have occurred decades ago,'' he said, "and whether or not it's admitted to the jury it has now -- through the press coverage -- tainted the potential jury pool for fair and unbiased jurors.''

Prosecutors could have opted for a closed filing, Mills said, to let the court rule on admissibility of the evidence "but for reasons unknown to the defense, they chose not to.''

Shirley is accused of kicking and stomping Mark Daniel Haines after a December 2010 police chase and falsifying records during a subsequent investigation.

Judge John Preston Bailey has scheduled Shirley's criminal trial for Jan. 22 in Martinsburg. A separate civil lawsuit is tentatively scheduled to be tried this fall.

Shirley, who was re-elected in November, has denied any wrongdoing and vowed that he will be vindicated. Haines, meanwhile, is serving a 19-year sentence for bank robbery.

The notice to the court says prosecutors will also introduce two video recordings from May 30, 2012, that show Shirley and another uniformed officer in what appears to be a booking room. The nature of the discussion on one video was not revealed. Prosecutors say the other tape has no audio.

The transcript, meanwhile, is from a sentencing hearing that former U.S. District Judge Craig Broadwater was holding in a separate case.

Shirley, a lieutenant with 23 years of service at the time, was testifying for prosecutors when he was questioned about his dealings with a man named Scott Rind over a piece of furniture that Rind had allegedly refinished and sold, knowing it belonged to Shirley.

Shirley testified that his wife, Debbie, had cheated on him with Rind years earlier.

"I was working one day, and I drove up on them and caught them in the act,'' he testified. "I shot at him one time, and that was it.''

An attorney then asked if he typically shoots people who are sleeping with his wife while he's on duty.

"Well, I had never been faced with that before, but I did that time,'' Shirley responded. "I don't typically, no.''

Shirley and his wife later divorced.