Veteran counterterrorism officials said they were convinced the plot was potentially serious, based largely on their emerging suspicions about Mr. Zazi, his training in explosives, his travel to Pakistan tribal areas where Al Qaeda is influential and the apparent ease of his movements within the United States.  But these officials, in Washington, New York and Denver, acknowledge that they could be overstating Mr. Zazi’s significance because they know little about his precise intentions and may never know completely what he might have been planning. But as the investigation has progressed there appear to be few doubters within the government.  The criminal complaints filed by federal prosecutors in Denver and Brooklyn charge that Mr. Zazi and the two others arrested, his father, Mohammed Wali Zazi, and the imam, Ahmad Wais Afzali, who was said to have been a source for the New York police, lied during questioning in the terrorism investigation.  On Wednesday, the complaints 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 them.  In the days leading up to his arrest, before he voluntarily underwent three marathon sessions of questioning by F.B.I. agents in Denver, Mr. Zazi, in interviews with reporters and through his lawyers, denied any links to Al Qaeda, any involvement in any plot and any wrongdoing whatsoever. On Sunday, after the announcement of the charges, neither his lawyer, Arthur Folsom, nor a public relations adviser whom Mr. Folsom had hired to field the seemingly endless barrage of calls from reporters, would comment.  The complaints are said by authorities to be a preliminary step that enabled them to detain the men, who had known for more than a week that they were under investigation.  What has troubled federal prosecutors and the F.B.I. is the belief that Mr. Zazi embodies what concerns them most: a Westernized militant, trained by Al Qaeda in Pakistan, whose experience and legal resident status in the United States give him the freedom to operate freely, yet attract little attention.  But the questions about Mr. Zazi’s significance continue to persist in part because the surveillance of him and others, including wiretaps and physical surveillance, was interrupted before authorities had obtained crucial information, like the intended target or the timing of any plot.  Mr. Zazi and his father 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.  Ibrahim Hooper, spokesman for the Council on American-Islamic Relations, a Washington-based Islamic civil rights and advocacy group, said in a telephone interview that the charges raised concerns about civil liberties.  “It heightens our concerns about the case because you would expect that if the government’s allegations were based on strong evidence, that there would be charges brought based on terror-related evidence, not making false statements,” he said.  Various court documents showed that investigators had removed what may be evidence from an apartment in Queens where Mr. Zazi stayed the night of Sept. 10, including backpacks, cellphones and a battery-powered scale that had Mr. Zazi’s fingerprints on it — suggestive of a possible bomb plot.  At the apartment where the objects were removed, a tenant, Naiz Khan, said the F.B.I. had questioned him about the scale, but he said he told them that it did not belong to him or any of his roommates.  “I don’t know who it belongs to,” he said. “This is not our scale. Maybe they got it from another apartment.”  In a sense, the case reflects the tension that has grown between intelligence and law enforcement agencies since the September 2001 attacks. Some intelligence officials are prepared to disrupt a group as soon as its activities are discovered, while more case-oriented law enforcement agencies seek to surreptitiously track or infiltrate a suspect group, uncovering all of its members, until there is compelling evidence to charge the plotters with a crime.  In this case, officials say, Mr. Zazi and his confederates were apparently deterred before any plot had a chance to take shape and before investigators were able to clearly understand what the men were planning. That left prosecutors to charge the three men with proxy offenses of making false statements rather than crimes directly involving terrorism.  Some officials said they had moved quickly, fearing that Mr. Zazi’s plans might have been more advanced than they realized, at the same time counterterrorism officials in New York were preparing for major events like this week’s meeting of the United Nations General Assembly, to be attended by President Obama and other leaders.  Al Baker and Karen Zraick contributed reporting.  A version of this article appears in print on , on Page A1 of the New York edition with the headline: Terror Suspect Had Bomb Guide, Authorities Say. Order Reprints| Today's Paper|Subscribe
A man arrested in Colorado had been trained in weapons and explosives in Pakistan, according to court papers.