Controversy continues to swirl around Rep. Gary Condit as new revelations about his affairs emerge from a flight attendant who says she was Condit's lover and from a man who says his 18-year-old daughter also had an affair with the congressman.

Statements made by flight attendant Anne Marie Smith have stirred particular interest among federal officials, who have opened an initial criminal inquiry into whether the California Democrat obstructed justice or encouraged perjury in the investigation of Chandra Levy's disappearance, according to the Associated Press.

Authorities specifically are looking at Smith's claim that Condit urged her to sign a statement denying their 10-month affair. Smith also says Condit told her she did not have to cooperate with FBI agents.

"It is in the preliminary stages, talking to witnesses and trying to determine if we should proceed further," an official familiar with the matter told the Associated Press, speaking on condition of anonymity.

Washington police on Thursday began a search of vacant buildings in the nation's capital, looking for clues in the disappearance of Levy, the 24-year-old federal intern who has not been seen since April 30. Condit has told police he had an affair with Levy.

"We have to explore the possibility that she may be dead and we're looking for the remains," said Terrance Gainer, Washington's No. 2 police official. "So we're looking at about one-seventh of the District of Columbia right now, at abandoned buildings.

"Our officers begin walking through those buildings today and we may use cadaver dogs if it's necessary," Gainer said on CBS' The Early Show.

Gainer said investigators are still working on four theories in Levy's disappearance: that she was a victim of foul play, that she committed suicide, that she walked away voluntarily or that she is wandering around not knowing who she is.

In the afternoon, about a half-dozen searchers carrying shotguns and crowbars used power drills to enter an abandoned building on the corner of Tenth and Euclid Streets. Police emerged after about 30 minutes and said they had evidence that someone was living in the building, but found no sign of Chandra.

Washington police 3rd District Commander Mark Beach said the searches would likely last through the weekend. He said some of the buildings were being searched for the second time. 

Police and the FBI are analyzing evidence uncovered in a search of Condit's Washington, D.C., home early Wednesday morning.

Law enforcement sources tell Fox News they found what appear to be several specks of blood on a Venetian blind in the Democrat's apartment, which will be analyzed by the FBI. Police also found what could be blood on another item.

But sources said that, if the evidence turns out to be blood, it is a small amount and police doubt it would be a remnant of any possible crime that took place two months ago.

Smith, the 39-year-old flight attendant who says she had an affair with Condit, told Fox News on Special Report With Brit Hume Wednesday that she believed the congressman knew more about Levy's disappearance than he was letting on.

"I think as a result [of coming forward] there's been, kind of, an impetus, a little more pressure on him to admit things," Smith said. "And clearly, asking me to sign the affidavit [that there was no affair], kind of, puts a shadow on his credibility."

Police, meanwhile, are continuing in their attempt to arrange for Condit to take a lie-detector test.

Gainer said he talked Wednesday with Condit's lawyer, Abbe Lowell. "The congressman's attorney has suggested we can get to a polygraph," Gainer said.

The Washington Post reported Thursday that FBI agents have interviewed a Pentecostal minister in California who says his then 18-year-old daughter had an affair with Condit.

The minister, Otis Thomas, was quoted by the Post as saying that Condit had told his daughter never to speak of the relationship. Thomas said his daughter is afraid to talk with the FBI and has gone into hiding.

Thomas, whose church is in Modesto, Calif., did gardening work at the Levy home in Modesto, the Post said.

Thomas told the Post that his daughter met Condit at a political rally and ended the relationship about seven years ago.

Addressing the most recent allegation, Condit spokeswoman Marina Ein told Fox News: "This is an example of what has occurred because of the media frenzy surrounding this story." She added that "rushing to publish every allegation is destructive," and said "Rep. Condit deserves better."

Chandra's father, Robert Levy, said Thursday that he and his wife, Susan, "know Rev. Thomas and we do appreciate his concern." He added, "Right now we can't really comment more on that."

Asked about the report, Gainer would say only that "the names and stories aren't unfamiliar to us."

Marina Ein, a spokeswoman for Condit, said the Post report was "discountable — there's no confirmation from the principal," referring to the daughter.

Asked if she was denying the congressman had an affair with the woman, Ein said: "We're not going to get in the territory of accounting for each and every one of the tabloid cases that are presented."

Attempts were unsuccessful to locate Thomas in Modesto, or reach him by telephone at a number of possible home and church numbers.

The Post and CNN, citing police sources, reported police have asked three other men to take polygraph tests. One said he occasionally socialized with Levy, but the connection of the other two to Levy was not immediately clear.

Several items taken from Condit's apartment during a late-night search that ended at 3 a.m. Wednesday were to be sent to the FBI crime lab in Quantico, Va., said Sgt. Joe Gentile, a Washington police spokesman.

Condit was at home while investigators searched his apartment, a day after Lowell said his client would allow police to conduct the search.

Levy was last seen canceling her membership at a Washington health club. Her internship had just ended, and she was planning to return home for graduation ceremonies at the University of Southern California.

Police searched her apartment and found nothing missing but her keys. Her bags were packed.

Condit, 53 and married, told police last week that he had an affair with Levy, according to a source familiar with the investigation. His staff had claimed for weeks that they were just goods friends.

The disappearance still is being treated as a missing-person case and police have said repeatedly that Condit is not a suspect.

While police looked for new information, the FBI and the U.S. attorney's office again questioned Smith. She has contended Condit asked her to sign a statement denying a 10-month affair she says they had.

Authorities declined comment on the questioning.

Smith said on Special Report that investigators indicated she had provided them with new information during the six hours she met with them. She would not disclose what she told them, but said she would meet with them again Thursday.

Smith said she and Condit never talked about Levy. She said she last spoke to Condit two weeks ago and that he again urged her to sign the statement.

Condit has not commented on any relationship with Smith, but in a statement last week said he never asked anyone to lie.

Fox News' Rita Cosby and The Associated Press contributed to this report.