NASA technicians analyzed data from the shuttle's last moments, searching for the cause of the tragic end of the 16-day scientific research mission.
NASA shuttle program director Ron Dittemore said data showed an increase in temperature from the left side of the shuttle and increasing drag on the left wing minutes before contact was lost. He said the drag could have been caused by rough or missing tiles, which protect the spacecraft from the 3,000-degree Fahrenheit temperatures of atmospheric re-entry.
But he said it was too soon to say what caused the disaster.
"I want to be careful that I don't jump to conclusions because if I do I'll miss something else that may be very important," he said.
In Washington, the White House announced President Bush and first lady Laura Bush would attend a memorial service Tuesday for the crew of space shuttle Columbia at the Johnson Space Center in Houston.
The shuttle crew included commander Rick Husband, pilot Willie McCool, flight engineer Kalpana Chawla, payload commander Michael Anderson, payload specialist Ilan Ramon, and astronauts David Brown and Laurel Clark. Ramon, McCool, Brown and Clark were making their first flights into space. Husband, Chawla and Anderson each had made one previous spaceflight. Ramon was Israel's first astronaut.
White House spokesman Ari Fleischer reiterated the president's commitment to finding the cause of the disaster and continuing space exploration.
"From the president's point of view," said Fleischer, "the mission of science and the marvels of space exploration will go on. He wants to make certain that every angle, every reason, every possibility of how this happened will be independently reviewed."
A retired Navy admiral, Harold Gehman Jr., was appointed to lead the investigation. He was a co-chairman of a Pentagon team that investigated the suicide bombing of the USS Cole in October 2000.
On Monday, Bush planned to meet with NASA Administrator Sean O'Keefe. He also instructed O'Keefe to brief the 16 chairmen and ranking minority members on key congressional committees that oversee the space program.
In Texas, searchers scoured a 100-mile-long path of wreckage southeast of Dallas, looking for debris for collection by federal authorities. Officers secured hundreds of pieces of debris and special teams collected human remains at the end of the debris field in Nacogdoches and Sabine counties near the Louisiana state line.
"There have been some remains here and in some other of the counties but we don't want to go into any other further detail," Nacogdoches County Sheriff Thomas Kerss said, adding that he was acting out of respect to the families.
Remains were also found in Sabine County to the southeast of Nacogdoches, a town of about 32,000 that appeared to be where most of the debris rained down. About 1,200 debris sites were identified in Nacogdoches County.
"Nobody is picking up that material right now," said County Judge Sue Kennedy. "GPS (Global Position Satellite tracking) is being used to pinpoint each site and it will be a federal agency that will go out and pickup debris."
Debris included a 7-foot piece of metal, circuit boards, spacesuit mission patches -- and an astronaut's helmet. James Couch of Norwood in San Augustine County found the helmet on his property.
"It's just a regular space helmet," he told The Dallas Morning News. "It's intact. The only thing that's missing is the shield that goes on the front."
The shuttle tragedy was the theme of religious services across the country Sunday. Near some of the debris sites, residents placed American flags and crosses in memory of the fallen astronauts.
In the small eastern Texas community of Hemphill, FBI agents took custody of what appeared to be the remains of one astronaut, Sabine County Emergency Management Coordinator Bill Smith told United Press International.
"There definitely is a lot of debris," Smith said late Saturday. The largest shuttle piece, he said, was "the size of a small vehicle."
NASA ground control teams in Houston lost tracking and radio contact with Columbia at 8 a.m. Saturday. Witnesses across Texas heard a sonic boom --some saying it was exceptionally loud and extended -- that typically signals a shuttle re-entry into the atmosphere, but then saw a flash and fiery streaks as debris fell to ground.
The spaceship was soaring at about 12,500 mph at an altitude of about 207,135 feet over north Central Texas when communications ceased during the phase of re-entry of maximum dynamic pressure on the space vehicle, NASA said.
The last radio call to the crew was a report from Mission Control a few minutes from what would have been a Cape Canaveral landing, a transmission about a shuttle tire pressure warning. There was one word of acknowledgment from the shuttle, then only crackling static.
The presence of an Israeli astronaut on the mission heightened security for the launch and flight, but the White House and O'Keefe said Saturday there was nothing to indicate a malicious act caused the shuttle's disintegration.
"At this time we have no indication this mishap was caused by anything or anyone on the ground," O'Keefe said. A White House official, speaking on background, also said there was no reason to believe the shuttle breakup was anything other than an accident. "There is no reason to believe there are any links to terrorism, but we are fully investigating," the official said.
Columbia lifted off Jan. 16 under tight security. Enhanced security was implemented following the Sept. 11, 2001, terrorist attacks in the United States.
The mission was the first of six planned for this year, with the remainder of the flights devoted to space station assembly. Thirty-two payloads aboard the Columbia, containing the results of 59 science experiments years in preparation, were lost.
The mood was somber and anxious in Israel, where residents all over the country had tuned in as the Sabbath ended to watch the landing of Israel's first and highly popular astronaut.
Israeli Prime Minister Ariel Sharon said, "The state of Israel and its citizens are standing at this difficult hour at the sides of the astronauts' families, the Ramon family, the American people and its government in a prayer to the almighty."
Indian-born Chawla, 41, had become a national heroine in 1997 in her first trip into space aboard Columbia. Indian Prime Minister Atal Behari Vajpayee led the mourning for the flight engineer, telling Bush in a message, "For us in India, the fact that one of them was an Indian-born woman adds a special poignancy to the tragedy."
The loss of the shuttle and the crew comes 17 years after the Challenger accident on Jan. 28, 1986, which claimed the lives of seven astronauts. It followed by 36 years the first fatal U.S. space program accident. On Jan. 27, 1967, three astronauts were killed in a flash fire during a test of the Apollo I space capsule.