A NASA research engineer warned two days before Columbia broke apart that the shuttle might be in "marginal" condition and that others in the space agency weren't adequately considering the danger of a breach near its left wheels, according to internal e-mails NASA disclosed Friday.

"We can't imagine why getting information is being treated like the plague," the engineer wrote in one of a series of messages describing internal concerns about Columbia's safety in the days before its breakup Feb. 1 over Texas.

Click to read the e-mail.

The board investigating the accident, which only obtained the e-mails late Friday, believes the shuttle suffered a breach based on its analysis of rising temperatures inside the same wheel compartment that the engineer had cited for concern.

The engineer, Robert Daugherty of NASA's Langley research facility in Hampton, Va., wrote two days before Columbia's breakup that experts on the shuttle's protective heat tiles were concerned that Columbia's condition was "survivable but marginal" after it was struck by debris on liftoff.

Other documents NASA released showed engineers feared that Columbia was struck on liftoff by three pieces of loosened insulating foam, not just the one previously acknowledged. NASA spokesman Allard Beutel said Friday that officials now believe one large foam piece broke into three smaller chunks before at least one struck the spacecraft. The investigating board said it was looking into the matter.

Daugherty did not mention in his e-mails any concern that a breach might cause Columbia to break apart during its fiery descent, saying that the risks of deadly heat burning into the wheel compartment was "arguably very unlikely."

But Daugherty explicitly warned in a Jan. 29 e-mail that "one of the bigger concerns" was that damage to thermal tiles near the wheel compartment seal could permit a hole there. He appeared worried most about pilots struggling to land Columbia with one or more tires inside damaged from extreme heat.

"It seems to me that if mission operations were to see both tire pressure indicators go to zero during entry, they would sure as hell want to know whether they should land with gear up, try to deploy the gear or go bailout," Daugherty wrote.

The accident board has previously determined Columbia almost certainly suffered a devastating breach along its wing and possibly its wheel compartment that allowed searing air to seep inside during its descent at nearly 12,500 miles per hour.

Earlier this week, board member James Hallock said investigators were "very much interested also in the landing gear door itself, because once again you have tiles all around the area, but you also have seals."

Unusual temperature readings inside the wing and wheel compartment began within minutes of the shuttle's re-entry, far off the coast of California.

Senior NASA officials have steadfastly supported assurances since the accident by The Boeing Co., a contractor, that Columbia was expected to be able to return safely despite the possible tile damage.

They also have maintained that concerns expressed in e-mails among midlevel engineers -- such as Daugherty -- were part of a "what-if" analysis, and that even these employees were satisfied with Boeing's conclusions.

"During the flight, no one involved in the analysis or the management team or the flight team raised any concerns," NASA spokesman James Hartsfield said Friday.

But the e-mails disclosed in Washington questioned some details about those assurances by Boeing, including underlying assumptions about the likelihood of minor damage from a large chunk of breakaway foam and whether injury to Columbia might have been caused by falling ice.

The e-mails also include references by Daugherty and another Langley employee, Mark J. Shuart, about secrecy over the studies of risks to Columbia. Shuart wrote Jan. 28 to two other employees, referring to the foam strike, "I am advised that the fact that this incident occurred is not being widely discussed."

The e-mails, which were not passed to senior mission controllers in Houston during Columbia's flight, will be turned over to the board investigating the accident, board spokeswoman Laura Brown said. All seven astronauts died in the accident.

The e-mails had been sought since last week by news organizations under the Freedom of Information Act. Employees at NASA's headquarters here published them Friday on the agency's Web site.

Last week, NASA disclosed a similar, worrisome e-mail by Daugherty. He wrote two days before Columbia's breakup about risks to the shuttle from "catastrophic" failures caused by tires possibly bursting inside the wheel compartment from extreme heat.

Daugherty was responding in that e-mail to a telephone call Jan. 27 from officials at the Johnson Space Center asking what might happen if Columbia's tires were not inflated when it attempted to land.

In other documents released Friday, a newly disclosed Boeing report said cameras saw three large pieces of debris, up to 20 inches long, that shattered into a shower of particles after striking Columbia along its left wing. The report, among those supporting Boeing's assurances to NASA that Columbia could return safely, was dated eight days before the spacecraft broke apart.

"Multiple pieces of debris were seen emanating from the ET (external tank) bipod area and later seen impacting the orbital lower surface," it said. "Three pieces of debris were observed."

Earlier Boeing reports during Columbia's flight had focused on possible damage from "a large piece of debris," also about 20 inches.

Brown, the spokeswoman for the investigating board, said that board members asked NASA for new details about the path of that debris and will again review films of Columbia's liftoff. She said the board also was investigating whether any metal materials might have shaken loose on liftoff and been revealed in the shuttle's plume through a specialized photographic analysis.

NASA released three reports Friday analyzing possible damage to Columbia's insulating tiles. News organizations had previously obtained two of these. The third, dated Jan. 24, indicated the highest risk of damage was along the leading edge of Columbia's left wing, based on the speed and on the angle of the strike as the shuttle roared skyward.