Police briefly roped off an area around Klingle Mansion in D.C.'s Rock Creek Park Monday afternoon as they searched for clues to the whereabouts of former federal intern Chandra Levy.

Computer records indicate that the 24-year-old looked up a map of the mansion, which is about two miles from her apartment building, as she used the Internet from her laptop on the morning of May 1, one day after she was last seen.

Levy was online from about 9:30 a.m. to about 1 p.m. that day, and also looked up travel Web sites and sent e-mails to friends and her parents.

Police apparently responded at 4:30 a.m. that morning to a 911 call reporting a woman screaming in Levy's building, but found nothing amiss. There were no signs of foul play in Levy's apartment after she went missing.

Levy's family believes that because her wallet, credit cards and identification were left behind, she must have left her apartment on May 1 with someone she knew, her parents' lawyer said Sunday.

Billy Martin, the Levy family lawyer, said on NBC's Meet the Press that Levy commonly didn't carry identification when meeting her "secret lover."

"Chandra instructed friends and family ... that that was the procedure used," Martin said. "He did not want her to be identified."

He added that Levy "appears to have been lured, called or brought out of the apartment expecting to return."

Washington Police Chief Charles Ramsey had a similar assessment on CBS' Face the Nation, saying that Chandra, last seen April 30, was "a pretty cautious woman and just wasn't one to just throw her door open to anybody."

"I mean, it just doesn't fit that it would be a stranger or something like that," Ramsey said.

After the Levy case was given prominence on the Fox network's Saturday broadcast of America's Most Wanted, a tip was phoned in that a van in the Dupont Circle area had been seen trying to lure women into it. Deputy Police Chief Terrance Gainer said that police would look into that.

The missing person's case has generated national attention because Rep. Gary Condit, whose district includes Levy's home town of Modesto, Calif., acknowledged to investigators that he was having an affair with Levy, a police source has said.

Condit, 53 and married, is not a suspect in Levy's disappearance, police have said. He has kept a public silence, and only acknowledged the romantic relationship in his third interview with police on July 6, the source said.

That reported admission prompted the Senate's top Republican, Trent Lott of Mississippi, to say that Democrat Condit should resign.

"Infidelity is always unacceptable, but particularly when you have an elected official involved in a position of trust with a young girl, an intern," Lott said on Fox News Sunday. "If these allegations are true, obviously he should resign. And if he doesn't, the people of his district probably will not re-elect him."

Rep. Christopher Shays, R-Conn., disagreed, telling CNN's Late Edition: "If infidelity is the test, there'd be a number of members of Congress that should resign."

Ramsey said investigators have not ruled out the possibility that Levy may have left her apartment without ID for other reasons, for example, to make a quick trip to a nearby store with only the money in her pocket.

Police have four theories: she left of her own accord, committed suicide, has amnesia or is the victim of foul play.

Police say the suicide theory becomes more unlikely with each passing day because a body has not been found. Last week, police released computer-generated pictures of Levy showing how she might look if she changed her hairstyle.

Levy was last seen when she canceled her membership at a health club. She was making preparations to return home to attend her graduation ceremony at the University of Southern California.

Under pressure from the Levy family, Condit took a polygraph test last week at the direction of his lawyer, Abbe Lowell, and without police investigators present.

The results of the test have been sent to D.C. police. Condit's office said that the delay in sending polygraph materials was the result of "copying issues."

Investigators will also ask Condit to submit to a polygraph test administered by police, but Ramsey said he is not hopeful the lawmaker will agree.

Marina Ein, a spokeswoman for Condit, said: "The appropriate thing to do is wait and see what the police say when they've had a chance to evaluate the polygraph the congressman took."

The Associated Press contributed to this report