NACOGDOCHES, Texas -- A hatch door and two other large pieces of debris were located as volunteers combed a vast wooded area in hopes of helping investigators piece together what is left of space shuttle Columbia.
More than 1,500 volunteers searched Sunday, but 500 or more were expected to return to jobs around the region Monday as the work week begins, the U.S. Forest Service said.
Incident co-commander Mark Ruggiero said the search was still "slow-going."
"The volunteers are a great help but a lot of folk coming from the city, they're not used to walking in the woods," Ruggiero said.
In Nacogdoches County on Sunday, three large shuttle pieces - including one that appears to be a hatch door - were located.
Nacogdoches County Sheriff Thomas Kerss said he did not know where on the shuttle the hatch may have been, but said it was "fairly heavy."
So far, the most significant shuttle parts recovered since Columbia broke up high over Texas on Feb. 1 have been a 2-foot long section of wing and a covering for a landing gear hatch. If they came from the left side, where sensors showed heating in the final moments, they could hold vital clues to what went wrong.
The pieces found Sunday were in the main debris path, in the piney woods in the eastern portion of the county.
Kerss did not have any details on the other two pieces, but said they were located in a remote area.
Another location of possible human remains had been found in the county, making a total of 10 possible sites there so far, Kerss said.
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