The Fairfax County judge in the next murder trial of sniper John Allen Muhammad did nothing wrong by traveling to Prince William County last week to investigate the case and should not recuse himself from the trial, Muhammad's lawyers argued yesterday.

Fairfax prosecutors filed a motion last week demanding that Fairfax Circuit Court Judge Jonathan C. Thacher step down from the case, after they learned that Thacher had journeyed to Manassas in an apparent attempt to resolve a complicated legal issue in the case. Thacher has not ruled on the motion and declined to comment.

But Muhammad's attorneys, Peter D. Greenspun and Jonathan Shapiro, said Thacher's actions shouldn't have been surprising because the judge had asked prosecutors to supply him with documents in the case and indicated that he would get them himself if they didn't.

The defense team also said the prosecution's claim that Thacher interviewed potential witnesses in Manassas, in advance of a hearing set for next week, was overblown and didn't require his recusal. Greenspun and Shapiro said the prosecution's true motive in trying to toss Thacher off the case was that the judge is seriously considering a defense motion to dismiss the case for violation of Muhammad's right to a speedy trial.

Fairfax prosecutors declined to comment yesterday.

Fairfax is seeking a second set of convictions against Muhammad, 43, in case his first convictions, won by Prince William prosecutors, are overturned on appeal. Muhammad was sentenced to death last fall on two counts of capital murder for his role in the October 2002 sniper shootings in the Washington area that killed 10 people and wounded three others.

Muhammad was indicted in both Prince William and Fairfax shortly after his arrest in October 2002. He was tried first by Prince William, and held in jail there, while Fairfax tried his accomplice, Lee Boyd Malvo.

But Muhammad's lawyers argued that Virginia law requires a jailed defendant to be tried within five months. They said that once Muhammad was brought to the state, in November 2002, his speedy trial clock began ticking. The prosecution responded that the five-month clock didn't begin until he was arrested on the Fairfax charge, which they said occurred in May of this year.

After both sides filed briefs on the issue, they argued it before Thacher on Aug. 30. At the hearing, Thacher twice asked Fairfax Commonwealth's Attorney Robert F. Horan Jr. for a copy of the county's "detainer" on Muhammad, a request from one county to another that a prisoner be held. Thacher's inquiry seemed related to Greenspun's citation of a 1993 appeals court case ruling that once a county filed a detainer with another county, it served as arrest authority and started the speedy trial clock.

Horan said he thought Fairfax had merely mailed a copy of Muhammad's indictment to the Prince William jail and had not sent a teletype or other detainer. Thacher then said, "I can get it from the Prince William court."

In the following days, Muhammad's attorneys provided documents from the jail appearing to show that both a faxed and a teletype detainer had been sent from Fairfax to the Prince William jail in January of this year and served on Muhammad. Horan responded that the Prince William jail officers, who are not sheriff's deputies, did not have arrest authority. In a Sept. 3 motion, the prosecutors asked for an evidentiary hearing on the issue.

On Sept. 7, according to prosecutors, Thacher traveled to Prince William and reviewed the jail file himself and spoke to jail employees. Prosecutors said the move violated state canons of judicial conduct and requested that Thacher disqualify himself. Legal experts said the trip was highly unusual.

Greenspun and Shapiro said the prosecution's failure to provide the judge with the documents he wanted "caused the Court to act . . . as he told the parties he would on Aug. 30 by cutting out the middle man and simply looking at the original documents."

The defense said the visit to the Prince William courthouse was not secret. They said that the judge was accompanied by a Fairfax sheriff's deputy and that a Prince William court administrator watched Thacher review the jail file, which apparently was delivered to the judge from the nearby jail.

The prosecution's claim that Thacher interviewed potential witnesses was "exaggeration and out of context," the defense said, and involved only conversation with the file's custodian about jail paperwork processes.

When the details of Thacher's actions are on the record, Greenspun and Shapiro said, "all question of impartiality will be put firmly to rest. There simply is no reasonable basis to question the Court's impartiality."