The Sept. 11 commission (search) failed to pursue information that a secret military unit had identified two cells involved in the 2001 terrorist strikes more than a year before the attacks, an Army intelligence officer contends.

Lt. Col. Anthony Shaffer (search) said that in January 2004, the commission declined to take up his offer of assistance.

"I just walked away shocked that they would kind of change their mind, but I figured someone with equal or better knowledge ... probably came and talked to them, so they must've taken care of it," Shaffer told The Associated Press in an interview Wednesday.

The information Shaffer said he gave during a 2003 meeting in Afghanistan was that the unit — known as "Able Danger" — had identified Sept. 11 ringleader Mohamed Atta (search) and three other hijackers as terrorist suspects.

The commission has denied that Atta's name or the name of any future hijackers were mentioned during the meeting.

Lt. Col. Chris Conway (search), a Pentagon spokesman, said Wednesday an investigation into Able Danger was under way.

The department "has been working to gain more clarity on this issue," he said.

Al Felzenberg, spokesman for the commission's follow-up project, said the commission is awaiting the results of the Pentagon's investigation.

A statement Friday by former commission chairman Thomas Kean and vice chairman Lee Hamilton said the commission did not obtain enough information on the operation to consider it historically significant.

Shaffer said Able Danger identified Atta and three other Sept. 11 hijackers in 2000. But, he said, military lawyers stopped the unit from sharing the information with the FBI out of concerns about the legality of gathering and sharing information on people in the U.S.

"The lawyers' view was to leave them alone, they had the same basic rights as a U.S. citizen, a U.S. person and therefore the data was kind of left alone," Shaffer said.

Shaffer said he and a Navy officer disagreed with that and tried to set up meetings with the FBI, but each time the idea was rejected by lawyers from the Special Operations command.

"There was a feeling ... if we give this information to the FBI and something goes wrong, we're going to get blamed for whatever goes wrong," Shaffer said.

The statement by Kean and Hamilton said only Atta was mentioned to the commission staff as being identified by Able Danger. They were told by a Navy officer about Atta 10 days before the commission released its report in July 2004, but the officer did not have documentation to back it up, the statement said.

The statement also said the Navy officer's dates related to the pre-Sept. 11 whereabouts of Atta did not fit with what they knew.

Shaffer said Able Danger "wasn't about dates and locations. It was about associations and linkages. That's what the focus was."

Shaffer said Able Danger (search) identified the terrorists using data mining techniques. His relationship to Able Danger was first reported by The New York Times and FOX News Channel.

Shaffer's lawyer, Mark Zaid, said Wednesday that Shaffer does not have documentation related to Able Danger because his security clearance was suspended in March 2004 for "petty and frivolous" reasons. They include a dispute over mileage reimbursement and a charges for personal calls on a work cell phone, Zaid said.

Shaffer, an Army reservist, has been on paid administrative leave for the past 16 months, Zaid said. He was an active Army major during his involvement with Able Danger, Zaid said.

Several defense officials on Wednesday identified the Navy officer as Capt. Scott Phillpott. They discussed matters related to Able Danger only on the condition of anonymity because of the sensitive nature of the program and the investigation into it.

A Navy spokesman said Phillpott was declining requests to speak with reporters.

Phillpott is now assigned as a Navy staff officer with a program called "Deep Blue," which is developing futuristic concepts for naval warfare, officials said.

Rep. Curt Weldon, R-Pa., vice chairman of the House Armed Services and Homeland Security committees, has said the Sept. 11 commission did not adequately investigate the claim that four of the hijackers had been identified more than a year before the attacks.