NASA administrator Sean O'Keefe said Sunday an independent panel will decide the significance of e-mails by a NASA research engineer warning two days before Columbia broke apart that damage to the shuttle's insulating tiles might have left it in "marginal" condition.

"I'm going to live by that judgment from that independent group to tell us exactly what we could have, should have, might have, would have done had we known something differently," O'Keefe said in a televised interview.

Click to read the e-mail.

But O'Keefe insisted the e-mail discussions of the spacecraft were not unusual. "Those are the kinds of dialogues and debates that go on every single time, during every single mission," he said.

"We want to encourage that kind of dialogue and are looking at releasing everything and anything we can find in order to get the maximum evidence and facts together."

The engineer, Robert Daugherty of NASA's Langley research facility in Hampton, Va., wrote days before Columbia disintegrated that experts on the shuttle's tiles worried that the shuttle's condition had deteriorated to "survivable but marginal" after it was struck by debris on liftoff.

The critical e-mails were released after news organizations sought them under the federal Freedom of Information Act.

The shuttle came apart Feb. 1 over Texas. All seven astronauts died.

O'Keefe said in the TV interview that the cause of the accident has not been determined despite the determination that pieces of loosened insulating foam struck the spacecraft.

"Everybody is looking at every single possible permutation of what could have caused this," O'Keefe said.

A 10-member independent panel, headed by retired Adm. Harold Gehman Jr., is investigating the accident.