Nothing found so far in search for Chandra Levy

A police officer exits an abandoned building in northwest Washington.

WASHINGTON (CNN) -- Police began a full-fledged sweep Thursday of abandoned buildings in northwest Washington near the apartments of missing former intern Chandra Levy and Rep. Gary Condit.

Federal prosecutors, meanwhile, were considering launching a criminal investigation into whether the congressman obstructed justice by allegedly asking a woman claiming to be his former lover to lie about their relationship.

On Capitol Hill, Rep. Bob Barr, R-Georgia, became the first member of Congress to call on Condit to resign, saying Condit's actions in connection with the investigation of Levy's disappearance have "obstructed an ongoing police investigation."

"I believe he should resign rather than bring further discredit on the House of Representatives," said Barr in a statement released by his office.

VIDEO D.C. Assistant Police Chief Terrance Gainer updates CNN's Bob Franken on Levy investigation (July 12) Play video (QuickTime, Real or Windows Media) CNN's Martin Savidge reports on possible GOP challengers to Condit's Democratic seat (July 11) Play video (QuickTime, Real or Windows Media) CNN's Jonathan Karl says the controversy surrounding Condit has seeped into his political life (July 11) Play video (QuickTime, Real or Windows Media)   MORE STORIES • Lawmaker calls Condit 'good member of Congress'   • Senator says she urged Condit to go public   • Police search Condit's apartment     EXTRA INFORMATION Interactive timeline   Polygraph facts     RESOURCES On the Scene: Jonathan Karl on how the Condit story is playing on Capitol Hill   Message Board: The case of the missing intern     AUDIO Listen to D.C. Police Chief Ramsey 381 / 35 sec AIFF or WAV sound

Across town, police used cadaver dogs to search some of the structures, but no traces of human or animal remains were found. They expected to search throughout the night.

"They didn't find any evidence of her demise," said Assistant Police Chief Terrance Gainer.

One police commander called the search the department's "highest priority," and the District of Columbia police chief said the case is one of the most intense in his three decades of police work.

"This is probably the No. 1 case that we've had during my time here, and I've been policing for 30-some-odd years," said Police Chief Charles Ramsey. "It's on the O.J. Simpson-JonBenet scale, I would think."

In the widening probe, the FBI called in Anne Marie Smith, a flight attendant who has said she and Condit had an affair, for a second day of interviews at the U.S. Attorney's office.

Smith said last week Condit asked her to lie to authorities about their alleged affair by signing an affidavit saying they never had a romantic relationship. Condit responded with a statement denying he asked anyone to mislead authorities.

Sources said federal prosecutors are questioning Smith to help them decide if they should open a criminal investigation into whether Condit obstructed justice in the affidavit matter.

Smith met with an FBI agent, two District of Columbia police detectives and two U.S. attorneys for seven hours on Wednesday.

While the search of abandoned buildings was under way, police wrangled with a Condit attorney over the scope of a possible polygraph test for the lawmaker.

Ramsey indicated attorney Abbe Lowell and police had yet to reach an agreement on how such a lie-detector test might take place.

"Whether or not this will be a reality, I have absolutely no idea," Ramsey said. "The only thing I do know is this: If we can't have an interview in which we're able to ask the questions we want to ask, then there's no point in doing it."

Across the country, at the home of Levy's parents in Modesto, California, sheriff's deputies arrived to begin a 24-hour surveillance of the home at the couple's request.

Assistant Sheriff Zane Clark said a direct phone line is to be established inside the home to various investigating law enforcement agencies.

Back in Washington, Cmdr. Mark Beach said the extensive search started late Wednesday to "fully document all abandoned buildings."

It resumed Thursday afternoon with dozens of police "going systematically" through the buildings, said Beach. The process is likely to continue through the weekend.

One of the sniffer dogs helping police search abandoned buildings.

"It's the highest priority that we have right now," he said. "We will not leave any stone unturned."

Ramsey said there are several theories in the case: That Levy met with foul play, committed suicide, disappeared voluntarily or is wandering around without any memory of who she is.

Ramsey said police want to conduct some computer generation work, using pictures of Levy and altering her appearance in case she's "missing intentionally" and has changed her hair style or color.

Condit has been the center of news media attention because of his relationship with Levy, who was last reported seen April 30 at a Washington gym.

Her family said the 24-year-old former intern with the U.S. Bureau of Prisons had an affair with Condit, 53, a married father of two, and police sources said Condit confirmed in an interview with police that the two had a romantic relationship.

Even as new reports emerged about another alleged affair, Condit tried to stay above the media frenzy surrounding him. As he emerged from his Washington apartment Thursday morning, he ignored questions from reporters about whether he will take a lie detector test.

Condit leaves his condo and past a throng of reporters Thursday morning.

Condit -- holding his suit jacket, dressed in a crisp white shirt and tie and smiling -- got into his car. "Good morning, guys," he said. "Have a nice day!"

In another development, investigative sources told CNN that FBI agents have talked with a Pentecostal minister in Condit's Calfornia congressional district and want to talk with his grown daughter.

The Washington Post reported the Rev. Otis Thomas, who has a landscaping business, told investigators his daughter had an affair with Condit when she was 18 and that the congressman warned her never to speak of it. (More on the minister and his daughter)

Condit has never admitted publicly that any relationship existed between him and Levy beyond a friendship.

-- CNN National Correspondents Bob Franken and Martin Savidge contributed to this report.