Federal authorities arrested an airport shuttle bus driver and his father in Colorado and another man in New York City on Saturday night, charging them with lying to investigators about an alleged terrorist plot to detonate an improvised explosive against an unknown target in the United States.
Acting swiftly late Saturday after a week in which investigators worked intensely in New York and Denver to put together a case, F.B.I. agents arrested Najibullah Zazi, 24, his father, Mohammed Wali Zazi, 53, who both reside in Aurora, Colo., and Ahmad Wais Afzali, 37, who lives in Flushing, Queens.
The arrests indicated the case was rapidly accelerating and provided for the first time — in a sometimes confusing week of events — an explanation of why authorities were investigating the men and provided details about the alleged plot still under investigation in the United States, Pakistan and elsewhere.
In a statement issued early Sunday, David Kris, the chief of the Justice Department’s national security division, said: “The arrests carried out tonight are part of an ongoing and fast-paced investigation. It is important to note that we have no specific information regarding the timing, location or target of any planned attack.”
Affidavits filed in the case said that during a search of the younger Mr. Zazi’s rental car on Sept. 11, agents found a laptop computer that contained an image of nine pages of handwritten notes. The notes, according to affidavit, “contain formulations and instructions regarding the manufacture and handling of initiating explosives, main explosives charges, explosives detonators and components of a fusing system.”
Last Wednesday, the affidavits said, when agents interviewed Mr. Zazi in Denver, he falsely said he had never seen the handwritten notes and told agents that he had not written the notes.
In two additional interviews on Thursday and Friday, Mr. Zazi told agents that during a 2008 trip to Pakistan, he attended courses and received instruction on weapons and explosives at an Al Qaeda training camp in a tribal area.
The affidavits also said that the elder Mr. Zazi and Mr. Afzali, who was said to have been a source for the New York Police Department, also lied to investigators about their conversations concerning the younger Mr. Zazi and their knowledge of his activities.
The father and son were scheduled to make an initial appearance on Monday in Federal District Court in Denver and Mr. Afzali will make his appearance, also on Monday, in Federal District Court in Brooklyn. Government officials said the charges, which carry a maximum penalty of eight years in prison, were preliminary and were likely to be followed by an indictment with more detailed accusations as the investigation continues.
The Zazis and Mr. Afzali are from Afghanistan. The elder Mr. Zazi is a naturalized citizen, while Mr. Afzalie and the younger Mr. Zazi are legal immigrants.
Wendy S. Aiello, a spokeswoman for Arthur Folsom, the lawyer representing the Zazis, said both men were arrested late Saturday night.
“Their attorney is with them,” said Ms. Aiello, who declined further comment.
Earlier on Saturday, following three days in which the younger Mr. Zazi had been intensively questioned by the F.B.I., he declined to meet with its agents, as planned, she said.
“He’s at home,” she said earlier in the day, adding that no plea arrangement was being negotiated on Mr. Zazi’s behalf.
At the same time, The Denver Post reported on Saturday that Mr. Zazi said in a telephone interview that he had not admitted any link to Al Qaeda, to participation in insurgency training in Pakistan or to involvement in a terrorist plot.
Government officials briefed on the matter have said that as Mr. Zazi voluntarily answered questions on Wednesday, Thursday and Friday, he admitted that he had perhaps unwittingly crossed paths in Pakistan with extremists allied with the terrorist organization. There were also indications that Mr. Zazi underwent training in explosives and bomb-making while overseas.
“If it was true, they wouldn’t allow me to leave,” Mr. Zazi told The Denver Post. I don’t think the F.B.I. or the police would allow anyone who admits being a terrorist to go free for one minute.”
In an investigation that went from covert to overt last week, the authorities were moving swiftly to check clues and track the movements of Mr. Zazi and those associated with him — even as they moved in federal court to file affidavits in support of the arrests.
On Monday, the authorities raided four residences connected to Mr. Zazi in Queens, and later executed search warrants his home in Aurora, and the home of his relatives there.
Investigators have copied or mirrored the hard drive of his laptop and are looking for e-mails, downloaded material and any trail of Internet sites that had been visited. The search of the hard drive did yield information about searches of sites connected to public gatherings in New York.
However, investigators have not yet determined what Mr. Zazi’s apparent interest in those sites suggests.
Attorney General Eric H. Holder Jr. has been briefed regularly on the status of the investigation, as has the F.B.I. director, Robert S. Mueller III, and officials at the White House and the Pentagon.
Aside from Mr. Afzali’s arrest, several people in New York have been questioned in the case. Three men at a fifth-floor apartment on 41st Avenue, in Flushing described how they had been interrogated on at least three separate occasions since their home was raided about 2 a.m. Monday.
Naiz Khan, 26, said he was interviewed for eight hours Thursday at what he believed was the Brooklyn offices of the United States attorney for the Eastern District. He said he voluntarily provided his fingerprints, DNA samples and prints of the soles of his shoes. A roommate, who spoke on the condition of anonymity, said he submitted to a similar interrogation.
Each man described how they were repeatedly asked series of questions about Mr. Zazi, who they said had spent the night of Sept. 10 sleeping in their apartment.
As they spoke in their home on Saturday, the men said they were not terrorists. Mr. Khan said he had spoken to Mr. Zazi only occasionally in recent years and the other man said he had yet to meet him. Mr. Khan said he doubted Mr. Zazi was a terrorist and expressed frustration over the fallout from his visit.
“He put us into trouble,” he said. “Why do they have to bother me and my roommates? Why do they have to go to my father’s house?”
A defense lawyer with experience in terrorism cases in New York said that three men that he knew of who had had contact with Mr. Zazi had been questioned and fingerprinted by federal authorities.
Robert Nardoza, a spokesman for the United States attorney in Brooklyn, Benton J. Campbell, would neither confirm nor deny the questioning.
Mr. Khan said he had not retained a lawyer.
As he spoke he displayed a several pages of search warrants that agents left with him after the Monday raid. The court papers outlined two pages of items to be seized, specifying that they wanted anything to do with explosives or their building blocks: chemicals, fusing caps, timers or blasting caps, among other things.
But the papers also listed what the authorities left with: cellphones; a laptop computer; papers and notebooks with Arabic writing; tools; 100 tongue depressors; a Con Edison bill; immigration papers and nine backpacks.
New York police officers returned on Tuesday and took a green nylon suitcase from a back bedroom, said Mr. Khan. He said his uncle Faiz Mohammed had packed the backpacks into the green suitcase and was planning to bring them to Karachi, Pakistan, for his children and those of his brother.
Mr. Khan also said the authorities asked him whether he had gone to rent a U-Haul on Sept. 9 in Queens and he emphatically said he did not.
“They said, ‘Did you go to U-Haul?’ and I said, ‘No,’ ” said Mr. Khan. “ ‘Did you pack anything, did you store anything in the U-Haul?’ I said, ‘No.’ ”
Ronald L. Kuby, a lawyer, said that Mr. Afzali, an imam in a mosque in Queens, did not rent any truck from U-Haul, though he, too, was questioned by agents in the recent days.
“He has not been in a U-Haul facility since 2004, when he rented a truck to help move his family,” Mr. Kuby said.