Three lawyers unsuccessfully tried to prevent police from questioning John Lee Malvo on Thursday night, but legal experts said yesterday that likely would have no effect on whether the statements can be used against Malvo.

During the questioning, sources said, Malvo, 17, provided the first detailed admissions of his role in the Washington area sniper shootings that left 10 dead and three wounded last month. Sources close to the investigation said Malvo admitted that he pulled the trigger in several of the shootings -- including, one source said, the slaying of FBI analyst Linda Franklin in Falls Church on Oct. 17. Fairfax County prosecutors are seeking the death penalty against Malvo in that case, and Prince William County prosecutors are pursuing a capital murder charge against Malvo's alleged co-conspirator, John Allen Muhammad, 41.

Malvo's attorneys yesterday sharply criticized investigators for leaking information about Malvo's statements, and they questioned the tactics that led to Malvo's seven-hour interrogation by Fairfax homicide detectives and federal agents.

"The police are flooding the media and poisoning the jury pool," Michael S. Arif said, "with their own paraphrasing and subjective interpretations of statements made during an unconstitutional interrogation of our client." He declined to comment on specific allegations.

When Muhammad and Malvo were arrested Oct. 24, they were held on federal warrants. But the Justice Department dismissed the charges, and the two suspects were moved to Virginia, allowing police to approach the pair again before new defense lawyers were appointed.

In Fairfax on Thursday afternoon, a juvenile court judge appointed a criminal lawyer -- Arif -- to represent Malvo and a guardian ad litem to protect Malvo's interests. Arif said the paperwork on his appointment had not been formally entered Thursday, so he knew police would not let him see Malvo.

The guardian, Todd G. Petit, went to Fairfax police headquarters and demanded that all questioning of Malvo cease. A police commander took Petit's business card, said he would relay the request and ordered him out of the building, Petit said. A lawyer from the county public defender's office also tried to see Malvo.

At the same time, Malvo's attorney in Maryland, Joshua Treem, faxed a letter to U.S. Attorney Paul J. McNulty in Alexandria, instructing that no one speak with Malvo. But Treem technically was no longer Malvo's attorney, and he received no response.

Petit's presence probably was irrelevant, legal experts said, as long as Malvo was read his Miranda rights and signed a form acknowledging that he understood -- and was waiving -- his rights to remain silent and have an attorney present.

"All police are obliged to do is avoid coercing a statement," said Anne M. Coughlin, a University of Virginia law professor. "They have no obligation to the lawyer. The fact that they failed to tell Mr. Malvo his guardian had come, as long as they had given him the Miranda warnings, is not going to be a constitutional problem."

Ira P. Robbins, a law professor at American University, said that in a case such as the sniper shootings, "the police are making absolutely sure they cover themselves. You figure the prosecutors are advising them."

Todd F. Sanders, a former assistant Fairfax prosecutor, noted that "there's no constitutional right for a suspect to consult with his parent."