The agents arrived at the home of Najibullah Zazi late Wednesday afternoon and left at about 11:23 p.m. One of the agents told ABC News the squad was carrying out a search warrant but declined to comment further.
Agents came down the stairs from the third-floor apartment, some carrying paper bags and microwave-size objects wrapped in brown paper that were loaded into FBI vehicles. FBI officials would not comment on what they found.
Zazi, 24, pulled up to his apartment in a white SUV minutes later, at 11:30 p.m., fresh from a meeting at Denver FBI headquarters that lasted eight and a half hours. He declined to answer any questions and briefly struggled to open his front door, which had been forced open by FBI agents serving a search warrant earlier in the day.
"You know, I am so tired that I don't even have a minute to even talk for one second, sir," he said in response to questions from reporters at the scene.
Earlier in the evening, agents also finished a search at a house on Ontario Place in Aurora that records show is occupied by Zazi's aunt, Rabia Zazi. The door to the residence had heavy damage from being smashed open when agents arrived. Nobody answered repeated knocks on the door. FBI Special Agent Kathy Wright would not comment on details of the investigation, but confirmed that the two locations were the only ones searched Wednesday.
Zazi's attorney, Art Folsom, said he and his client met for more than eight hours Wednesday with investigators at FBI headquarters in Denver. Folsom described the questioning as cordial and detailed but declined to go into specifics. Zazi is scheduled to meet with the FBI again this afternoon.
Folsom insisted that his client is not under arrest and is not being called a suspect. He downplayed reports that bomb-making materials were found in Zazi's apartment.
"If they had found something, would you let a guy go if he's already sitting in your building?" Folsom said.
Authorities: Zazi Carried Bomb-Making Instructions
Zazi's travels to New York last weekend triggered a round of highly publicized raids in the New York City area. Authorities told members of Congress the raids had helped to disrupt a plot to carry out a major attack on New York.
Law enforcement officials said agents discovered 14 brand-new black backpacks in the New York raids, leading to concern the men may have been planning to use the backpacks to carry suicide bombs.
The men responsible for the attacks on the London subways and the Madrid commuter rail system used backpacks to carry their homemade explosives.
Authorities say Zazi brought with him instructions on how to build a bomb using household chemicals.
Zazi denied Tuesday that he had any connections to al Qaeda and said the FBI "got it wrong."
"I have nothing to do with al Qaeda," Zazi told ABC News' Denver affiliate. "Any link or anything with al Qaeda."
Zazi, an Afghan emigre who has lived legally in the United States since 1999, emerged at the center of the case Monday after FBI agents and local police carried out raids on three apartments in New York City where Zazi visited over the weekend.
No charges have been filed, but law enforcement officials told members of Congress they suspected Zazi and the plot were directly connected to al Qaeda, and that Zazi had frequently traveled to Pakistan.
Rep. Peter King, R-N.Y., said "there is very good reason to believe that there is a connection to al Qaeda or to al Qaeda supports.
"[Investigators] would not have moved as quickly as they did if they did not believe there was real potential," King said.
But, Folsom said, "My client is not a terrorist," adding "if anything, this is a matter of guilt by association."
Folsom described Zazi as a "quiet and shy young man" who works as an airport taxi shuttle driver in Denver. He said his client visits Pakistan because his wife lives there, in the city of Peshawar, near the Afghan border.
FBI: 'No Imminent Danger' to New York City
Zazi was stopped on the George Washington Bridge as he entered New York City last Thursday for what he was told was a routine drug inspection, although he had not seen any cars stopped before him, his lawyer said.
Two days later, police towed his car away for an alleged parking violation.
Appearing before a congressional committee Wednesday, FBI Director Robert Mueller said there is no "imminent danger" to New York after the raids.
In an apparent attempt to defuse reports of tension between the FBI and New York Police Commissioner Ray Kelly, Mueller said, "New Yorkers are well benefited by the work of the NYPD and Ray Kelly."
Several of Zazi's friends who were taken into custody, arrested and released during the raids said authorities have it all wrong.
"He was a very nice person," said Naiz Khan, a coffee cart operator in Manhattan who is an acquaintance of Zazi's and attended the same mosque in Flushing, Queens. "He's not dangerous, he's a kid. So he can't be dangerous."
Khan, an Afghan native, was arrested Monday but released after four hours with no charges.
Heavily armed police believed they might find a bomb-making facility during their raids, but no such materials were discovered, authorities said.
Asa Eslocker and Jason Ryan contributed to this report.