ASHINGTON, June 6 — When Zacarias Moussaoui was arrested last Aug. 16 in a Minneapolis hotel room, federal agents also took custody of the belongings that he left behind, including two knives, a pair of binoculars, a hand-held aviation radio and — tantalizingly — a laptop computer and a notebook.
Within days, the record shows, F.B.I. agents in Minneapolis became convinced that Mr. Moussaoui, a 33-year-old Muslim radical, was some sort of terrorist and that he might be planning to use his flight training in Minnesota to take command of a hijacked plane.
Without a court-approved warrant, the Federal Bureau of Investigation was barred from searching the computer for whatever secrets Mr. Moussaoui might have locked inside and from conducting a more thorough search of his other belongings. So the agents turned to bureau headquarters in Washington, seeking permission to go to court for the warrant.
But for nearly three weeks, the Washington supervisors refused, insisting that there was insufficient evidence to tie Mr. Moussaoui to a foreign power, the standard of evidence required for the search.
The increasingly frantic pleas of the Minneapolis office for a search of Mr. Moussaoui's computer and the adamant, repeated refusal of the bureau's Washington supervisors to act are now at the center of Congressional investigations into the intelligence and law enforcement failures that predated the Sept. 11 terror attacks.
Federal officials say that if Mr. Moussaoui's computer and other belongings had been fully searched before Sept. 11, the evidence might have led the F.B.I. to at least a handful of the hijackers.
The computer, they said, contained evidence of Mr. Moussaoui's new-found interest in piloting — and more specifically crop-dusting, which the Qaeda terrorist network had considered as a method of disbursing chemical or biological weapons. The notebook listed the alias and had a telephone number in Germany for a young Arab man now considered the paymaster of the Sept. 11 terrorists.
Coleen Rowley, the Minneapolis agent who was a star witness on Capitol Hill today as a result of her accusation that Washington supervisors hindered the investigation, said in a May 21 memorandum that without Washington's obstruction, "it's at least possible we could have gotten lucky and uncovered one or two more of the terrorists in flight training prior to Sept. 11, just as Moussaoui was discovered."
The struggle over the warrant did not end until the afternoon of Sept. 11, only hours after hijacked planes had slammed into the World Trade Center and the Pentagon, when the Minneapolis agents were granted an emergency criminal warrant to inspect Mr. Moussaoui's belongings.
While the bureau and federal prosecutors have never divulged the full contents of the computer, officials say it contained important evidence that will be used to prosecute Mr. Moussaoui as the "20th hijacker" in the suicide attacks, including flight-simulation software and the information about crop-dusting.
The notebook, they said, contained the phone number for an apartment in Hamburg, Germany, for Ramzi Muhammad Abdullah bin al-Shibh, the Yemeni man who the authorities say served as the paymaster for the Sept. 11 hijackers, as well as a handwritten reference to "Ahad Sabet," Mr. Shibh's alias.
In Mr. Moussaoui's other belongings, the agents also found a letter from a Malaysian computer company, Infocus Tech, offering a business reference for Mr. Moussaoui.
The letter was signed by "Yazid Sufaat, managing director," a Malaysian microbiologist who had been identified as an important Qaeda organizer in Southeast Asia. His condominium was used in January 2000 for a meeting of several Qaeda conspirators, including two of the Sept. 11 hijackers. The meeting was observed by Malaysian intelligence agents who later alerted the Central Intelligence Agency.
Before Sept. 11, the French government had also given evidence to the United States linking Mr. Moussaoui, a French citizen of Moroccan descent, to Muslim extremists in Chechnya.
In Ms. Rowley's memorandum last month, which became known to news organizations within days of its delivery to the F.B.I. director, Robert S. Mueller III, she said that the "reasonable suspicion" that Mr. Moussaoui was a terrorist "quickly ripened into probable cause" in mid-August "when the French intelligence service confirmed his affiliations with radical fundamentalist Islamic groups and activities connected to Osama bin Laden."
Her colleagues in Minneapolis, she said, "became desperate to search the laptop that had been taken from Moussaoui, as well as conduct a more thorough search of his personal effects — the agents in particular believed that Moussaoui had signaled he had something to hide in the way he refused to allow them to search his computer."
But Washington supervisors, she said, continued to "throw up roadblocks and undermine" the efforts to obtain the warrant. "HQ personnel brought up almost ridiculous questions in their apparent efforts to undermine the probable cause," she said.
The bureau has said the supervisors in Washington believed that the Minneapolis agents had not met a legal standard requiring that Mr. Moussaoui be tied to a foreign power, a term defined broadly in previous court cases to include international terrorist groups, before his possessions could be searched.
But Ms. Rowley said in the memorandum that the French intelligence information alone established that link clearly and that Mr. Moussaoui's links to terrorists became more obvious "with successive, more detailed information from the French and other intelligence sources."
Despite all of the evidence that appears to link Mr. Moussaoui to the Sept. 11 attacks, his court-appointed lawyers have suggested that they could still mount a strong defense, especially since Mr. Moussaoui had been in prison in Minnessota for nearly a month when the suicide hijackings were carried out.
Prosecutors, they say, have never released evidence showing that Mr. Moussaoui communicated with any of the hijackers before his arrest. "There is no evidence that Moussaoui ever communicated in any way with any of the 19 hijackers," said Edward B. MacMahon Jr., a defense lawyer.
In a telephone interview today, Mr. MacMahon would not comment on other elements of the case against Mr. Moussaoui, who is seeking to dismiss his court-appointed lawyers and represent himself. But in earlier court papers, his legal team was critical of the evidence tying Mr. Moussaoui directly to the Sept. 11 attacks.