AURORA, Colo. -- An Aurora man who is at the center of an investigation into a possible terrorist cell has been asked to return to FBI headquarters Friday for a third day of questioning.

The 24-year old man and his attorney spent 8½ hours with investigators Thursday before leaving the Federal Building through a side door to avoid waiting reporters.

Najibullah Zazi spent more than eight hours Wednesday with FBI agents and eventually submitted to providing DNA, fingerprints and handwriting samples.

Zazi's attorney, Art Folsom, said the questioning at FBI headquarters were cordial but very detailed. And they expect much of the same Friday when Zazi undergoes another day of questioning.

"My client has been answering all of their questions and I presume today we're just going to pick up where we left off yesterday. ... Our intent is to answer any questions they have and hopefully clear any suspicions they have about my client," Folsom said.

Folsom said Zazi was very forthcoming with the FBI and he didn't have to interrupt during the questioning. He said he only interfered once, when he stopped Zazi from answering one question -- and that was only because Folsom himself didn't know what the answer was. However, he said now that he's discussed the question with his client, Zazi would be answering any and all questions from the FBI.

Zazi met with FBI agents at 2 p.m. Thursday, after meeting with his attorney. Zazi didn't speak to the media on Thursday, but appeared tired and apprehensive.

"I am very tired. I had a long day, I am not going to answer any questions," Zazi said after returning home around 11:30 p.m. Wednesday.

His attorney said Zazi is not being called a suspect and he maintained no bombmaking materials were found in Zazi's apartment.

"There were no diagrams, no bombs, no information like that. We're here to continue working with authorities in an attempt to clear my client's name," Folsom said.

Folsom said if the FBI found any evidence of value, they would have held Zazi instead of releasing him each night.

"I think if the FBI had any reason to arrest him they, one, wouldn't have let him leave last night, and two, if they thought they found something in the course of the evening, I don't think they would have taken the chance on whether or not we were going to show up today at 2," Folsom said. "If I were an FBI agent and I found something incriminating, I would be concerned that Mr. Zazi might not show up today ... and I would go down and pick him up. But as you can see, that hasn't happened."

Folsom said Zazi is "simply somebody who was in the wrong place at the wrong time" and believes federal agents are "fishing" to find anything connecting Zazi to al-Qaida.

"It seems like the only thing that they have is that he was in New York and stayed in the home of somebody that they were watching," Folsom said.

During the searches by federal authorities, several boxes of items were removed, but Zazi and his attorney continue to deny any terrorist ties and any motivation to plan an attack against America.

"I have actually asked him those questions and several similar to it ... and (there's) a categorical denial of having any contact or connection with al-Qaida. He's not a terrorist. He's had no plans to do any kind of attacks or do any kind of harm or damage to this country or anyone in it," Folsom said.

Paper bags, luggage and microwave-sized objects wrapped in brown paper were removed from Zazi's home and loaded into FBI vehicles.

The FBI investigation has been under way for some time, but it came to light on Monday when federal agents raided and searched three apartments in New York. Investigators said police and the FBI had been watching Zazi because of suspected links to al-Qaida.

Zazi drives an airport shuttle and works with his father, his aunt said. She said he is too busy working to be affiliated with any terror groups.

Zazi's aunt said he recently visited the Peshawar region of Pakistan. where his wife lives. He hopes to bring to the United States. She said her nephew often travels to Pakistan to spend time with his wife. Folsom said Zazi spends three months of the year in Pakistan and has been to Pakistan four times. His last trip to Pakistan was last year, and Zazi returned to United States in January, Folsom said.

She said Zazi was born in Pakistan but moved to the United States at an early age and grew up in Queens. He moved to Colorado several months ago to help his father with his airport shuttle business, she said.

Law enforcement officials told The Associated Press that a joint FBI-New York Police Department task force had put Zazi under surveillance because of the suspected links to al-Qaida. They had tailed him from Colorado to New York and had been tracking him for months, apparently including the recent trip to the Pakistan, the officials told AP.

ABC News reported that in series of raids on Monday, agents seized 14 new black backpacks they suspect were to be used to carry suicide bombs, and instructions on Zazi's computers on how to build a bomb with household chemicals.

Local FBI officials aren't commenting on the investigation, but the executive director of the Homeland Security Program at the University of Denver's Korbel School of International Studies told 7NEWS that he's not surprised that the feds are investigating someone in Colorado.

"No, it doesn't surprise me," said Greg Moser, who worked in Air Force intelligence before moving to Homeland Security. "It's recognition of the fact that terrorism is not an event, it's a delivered criminal process."

"As we saw on 9/11, that event was planned and perpetrated all over the world. It didn't just focus on one area," Moser added.