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.
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.