NASA engineers confirmed the recovery of debris from the shuttle Columbia's left wing today amid reports one of the orbiter's four general purpose flight computers - or some sort of avionics box - might have been located.

NASA Administrator Sean O'Keefe said some 12,000 pieces of shuttle debris have now been recovered and that the first trucks carrying the spacecraft's remains should begin arriving at the Kennedy Space Center this Wednesday for reconstruction by accident investigators.

In the meantime, O'Keefe said, "there is no favorite theory" about what triggered Columbia's catastrophic breakup Feb. 1 as it flew across Texas on the way to a landing at the Kennedy Space Center.

"There is no preferred or optimal or more probable consequence or cause that we see," he said. "Everything is on the table."

The independent Columbia Accident Investigation Board, chaired by retired Navy Adm. Harold W. Gehman Jr., will hold its first news conference at 3 p.m. EST Tuesday. O'Keefe said the AIB will now take over day-to-day operation of the investigation as NASA assumes a support role.

"It's become a very methodical, very structured process to assure we aren't defaulting in the direction of one favored approach or one favored theory or one more today's vox populi theory versus another so that we're not then in turn seeing a trail that could have been pursued then start to grow a little cold as we work through it," O'Keefe said.

Michael Kostelnik, who oversees shuttle and space station operations at NASA headquarters in Washington, said search teams had confirmed recovery of a portion of Columbia's left wing, but it was not found just west of Fort Worth as originally stated. Instead, it was found about halfway between Fort Worth and Lufkin, Texas.

"They have at least one piece of the left wing," Kostelnik said. "Clearly, you have to understand when you go out in the field and look at this material, our own experts are having a difficult time determining what some of these objects are. We're not just finding them, we're cataloging them and bagging them to get them back to the reconstruction site (at Kennedy) just as quickly as we can."

So far, he said, no confirmed shuttle debris has been found west of Fort Worth.

Late today, NASA officials said search crews might have located one of the shuttle's four general purpose flight computers. Later still, however, they said they were not sure what had been recovered. Engineers are eager to recover any debris that might include intact computer memory, drives or tape, which might hold data that could shed light on what went wrong during Columbia's re-entry.

On another front, Kostelnik said photo analysts are attempting to enhance long-range imagery of the shuttle in hopes of more clearly showing what sort of damage the left wing might have suffered during re-entry. A low-resolution image of the shuttle released Friday clearly showed something amiss near the leading edge of the left wing, but NASA officials have said they do not yet have a sharper image in hand. Media reports today indicated such imagery does, in fact, exist.

"We have a couple of photo images that we're putting into small study groups to get the right kind of people looking to see what these things could be," Kostelnik said.

In addition, Air Force personnel are reviewing radar data indicating something might have broken away from the shuttle the day after launch. The object was discovered after radar operators, acting on a multi-agency request from NASA, reviewed stored data.

"This was a request to go back and run the tapes and see if any anomalies were observed," Kostelnik said. "In this instance, this piece of space debris, a characterization which has been accurately reported in the media, was found on the tape by the Air Force.

"They are continuing in the process now of trying to confirm their calculations that based on where it was when they found it, (where) based on orbital mechanics it would have backed up to be on the second day of the orbiter's mission in the general vicinity of the orbiter, so much that it could have been something associated with the orbiter. The Air Force is going back to reconfirm their calculations."

At the same time, NASA and Boeing engineers are reviewing telemetry from the shuttle "to take a look at everything we knew about that, was there anything that the crew noticed, were their any measurements on the shuttle that would have detected some impact or some movement. We're going into an incredible amount of detail with everything we know about that time period to have some sense of what it could be."

The radar data indicates an object suddenly moving away from Columbia at about 11 mph, raising the prospect of impact by high-velocity space debris that might have knocked off a piece of the shuttle. At this point, however, it's not known what might explain the observation.

Mike Mott, Boeing vice president and general manager for NASA systems, said more than 1,000 company employees are working on the shuttle recovery operation with clearance from senior management "to bring in whatever expertise we need."

"We've brought in some folks from commercial aircraft early who are experts in accident investigations and they understand about debris recovery and reconstruction of debris," he said in an interview. "I think they've been really key players in helping NASA.

"We've brought in some thermal experts, we've brought in some photo enhancement expertise and all sorts of things in aerodynamic modeling. We've got folks out in the field helping in debris recovery and obviously continuing all our normal, technical and engineering and analytical work here just trying to help in any way we can."