Tests show Columbia lost part of heat shield, investigators say.(The Dallas Morning News)

Byline: Pete Slover and Bruce Nichols

HOUSTON _ In a finding that comes tantalizingly close to an explanation for the loss of Columbia, radar tests indicate a key piece of the space shuttle's heat shield came off the left wing after it reached orbit, investigators said Tuesday.

The so-called "carrier panel" could have come from near the wing's leading edge, which analysts say may have been damaged by debris falling from the shuttle's external tank shortly after launch Jan. 16.

Investigators suspect the left wing was breached by the hot gases that envelope the shuttle as it plummets back into the atmosphere toward landing. Seven astronauts died ...