U.S. Sen. Bill Nelson said Friday that he will seek full disclosure of the information gathered by the board investigating the loss of space shuttle Columbia, even if Congress has to use its subpoena power to get it.

"I come from an experience of open government in Florida, and the thinking there is, 'The more that's in the sunshine, the more the truth is going to be there,' " said Nelson, D-Fla. "This is not a military matter. It's a civilian matter, and it's trying to fix a problem that is an American tragedy. It's not going to be credible with the American people unless it is made public."

The Columbia Accident Investigation Board, as it is formally known, has offered total confidentiality to the more than 200 witnesses interviewed so far as part of its military-style investigation into what caused the shuttle to break up over Texas on Feb. 1.

Harold W. Gehman Jr., the retired Navy admiral leading the board, maintains that talking to witnesses behind closed doors will yield "a deep, rich, complete" look at the National Aeronautics and Space Administration.

"It cannot be done any other way, in our opinion," he told the Senate Commerce Committee earlier this week.

But at that hearing, several senators -- including Nelson and Sens. John McCain and Ernest Hollings -- expressed concern that Congress would never see the complete picture of what went wrong with Columbia.

"It's extremely important that congressional oversight committees have access to all critical information in this investigation," McCain, R-Ariz., said during the hearing.

"I don't see this as a problem, meeting the oversight responsibilities of Congress in a way that's satisfactory to you," Gehman responded, adding that negotiations were under way between the board and Congress.

After the hearing, Nelson and McCain, the committee's chairman, said they were encouraged and would wait to see how the negotiations played out.

However, a proposal circulated by the board to senators and committee staff would allow only McCain and Hollings, the committee's ranking Democrat, and other members they select to see -- but not copy -- the testimony. And the testimony would never be released to the public, congressional sources said.

That proposal reignited Nelson's earlier fears. In a letter sent Friday to McCain and Hollings, of South Carolina, Nelson called on the two senators to reject the board's offer.

"I urge you to insist that the board publish the entire work product of its investigation with its final report," Nelson wrote. "If the board is unwilling to do so, the committee should issue subpoenas for these records and, once in possession of them, place them in the public domain.

"Secrecy may be policy in military investigations, but NASA is a civilian agency."

Nelson said he realizes that these demands may create problems for witnesses who have already testified. Though the board should never have granted confidentiality in the first place, he said, he's willing to try to accommodate witnesses who think their candor might endanger their jobs.

"There has got to be a process developed where those witnesses can review their statements and then re-certify them," he said. "It would be unfair to those who have been told one thing to come back and tell them another thing."

Nelson said he spoke with McCain and Hollings on Thursday and that they encouraged him to pursue broader access to the testimony.

A spokeswoman for McCain said Friday that her office had not yet seen Nelson's letter. Hollings spokesman Andy Davis said Hollings has been impressed with Gehman so far and is willing to wait and see what comes out of negotiations with the board.

"What Hollings' sense was is that there was going to need to be broader access for the committee," Davis said. "But how we handle that is still under discussion."

Laura Brown, the board's spokeswoman, said the board would have no comment while negotiations about access continued with Congress.

"Until we work out an agreement with the committee, I don't think we'd want to address what's in the letter, because some of those issues are what we're working on," she said.

The board has been able to offer witnesses anonymity because of a loophole in the Federal Advisory Committee Act, which generally requires appointed boards to publicly advertise their meetings, whether open or closed; keep minutes of all sessions; and generally make their records available to the public.

But the law exempts boards composed completely of federal employees -- and all 13 members of the Columbia board are on the federal payroll.

Seven, including four active-duty military officers, two federal transportation officials and an active NASA employee, were already working for the government. Five "independent" members are being paid $134,000 a year by NASA. Gehman gets $142,500 from another federal agency.

The salaries and the level of secrecy they allow, reported in the Orlando Sentinel last weekend, have raised eyebrows among supporters of open government.

Robyn Suriano of the Sentinel staff contributed to this story. Gwyneth K. Shaw can be reached at gshaw@orlandosentinel.com or 202-824-8229.