Federal investigators searched the wreckage of Wellstone's plane in Minnesota Saturday to determine why it crashed, as the state and political colleagues across the nation mourned the Democratic lawmaker.

Only the burned tail section of the private plane was still intact, Carol Carmody, acting chairwoman of the National Transportation Safety Board said Saturday. Everything else was destroyed.

Video: Feds Investigate Cause of Wellstone Crash

"It's a complicated site, very marshy, lots of trees," Carmody said. "It takes us time to sort through the evidence."

It appeared the engines were powered when the plane went down, but it likely will take weeks if not months to determine why the chartered twin-engine Beech King Air A100 crashed, Carmody said. She said there was no cockpit voice recorder.

Carmody said the team might spend up to six days at the site where the small plane crashed Friday, killing Wellstone, his wife and daughter, and five others. But she said the team was prepared to stay as long as it took to establish the cause.

The senator was on his way to attend the funeral of a state representative's father when the twin-engine private plane went down at about 10 a.m. in freezing rain and light snow near the Eveleth-Virginia Municipal Airport, about 175 miles north of Minneapolis. A pilot in the area said the plane seemed to have veered away from the usual approach to the airport.

"It's just terrible. Say a prayer," said Lisa Pattni, an aide at the crash site.

The wreckage was still smoldering several hours after the crash in a wooded, swampy area two miles from the airport and several hundred yards from the closest paved road.

The death brought an outpouring of grief from both supporters and opponents of the 58-year-old Wellstone, one of the foremost liberals on Capitol Hill. In St. Paul, thousands of mourners stood in a cold rain to pay tribute at the Capitol and outside the senator's headquarters. Many wept.

"It doesn't seem real," said Tom Collins, who had done volunteer work for the Wellstone campaign. "It's a nightmare."

All eight people aboard the 11-seat King Air A-100 were killed, said Greg Martin, spokesman for the Federal Aviation Administration. Campaign officials confirmed the victims included Wellstone's wife, Sheila, 58, and daughter, Marcia, 33; three campaign staff members; and two pilots.

The last senator to die in office was Sen. Paul Coverdell, a 61-year-old Georgia Republican who died of a stroke two years ago.

"Today the state of Minnesota has suffered a deep and penetrating loss," Gov. Jesse Ventura said. "With all of us suffering from the numbing experiences of our nation's recent tragedies, this loss seems especially cruel."

Wellstone's death threw the battle for the Senate into uncharted territory. Before Friday, Democrats held control by a single seat.

Minnesota law allows the governor to fill a vacant Senate seat, but it also allows a political party to pick a replacement if a nominee dies. In this case, the name must be offered by next Thursday.

Ventura wouldn't say what he would do, saying only that he would not appoint himself to serve the rest of Wellstone's term in the lame-duck session of Congress between Election Day and the arrival of new members.

Shaken Democratic officials wouldn't comment on possible replacements. Rebecca Yanisch, the state trade commissioner who ran for Senate in 2000, indicated she might be interested, while former Sen. Walter Mondale didn't take questions at an appearance and didn't return a call seeking comment.

"I just want to spend today mourning," Mondale, who will turn 75 in January, told The Washington Post for its Saturday edition.

Two years ago, Missouri Gov. Mel Carnahan, his son and an aide were killed in a crash three weeks before Election Day as he campaigned for the Senate. His name remained on the ballot and he beat Republican Sen. John Ashcroft. Carnahan's widow, Jean, was appointed to serve in his place and is now running in a special election against Republican Jim Talent, with the winner completing the six-year term originally won by Mel Carnahan.

Mrs. Carnahan canceled campaign appearances Friday and called Wellstone's death "heartbreaking news."

Wellstone was up against Republican Norm Coleman, a former mayor of St. Paul and President Bush's choice to challenge the two-term incumbent.

"The people of Minnesota have experienced a terrible, unimaginable tragedy," Coleman said.

At the site, FBI spokesman Paul McCabe said there was no indication the crash was related to terrorism. He also said it would take time to recover the bodies, which remained in the wreckage late Friday.

Ventura said flags at state buildings would be flown at half-staff through Nov. 5.

In Texas, Bush called Wellstone "a man of deep convictions."

"He was a plainspoken fellow who did his best for his state and for his country," the president said. "May the good Lord bless those who grieve."

Wellstone hated to fly, especially in small planes often used by politicians to fly to every corner of their states. His wife hated to fly too. Wellstone once told an audience he had a bad feeling about them flying in a small plane together.

Senator Mark Dayton says Wellstone "willed himself" to fly because he believed in what he was doing. A former campaign aide says fear was a daily presence, but he had no choice.

Democratic Rep. Collin Peterson of Minnesota said Wellstone wouldn't fly unless there were two pilots on board. The two pilots on board the 11-seat King Air A-100 were killed as well.

Also killed was a friend of Sheila Wellstone who often traveled with her to calm her fear of flying in small planes.  

Before running for office, Wellstone was a professor and community organizer who fused the two passions in a course he taught at Carleton College in Northfield called "Social Movements and Grassroots Organizing."

He stunned the political establishment by upsetting Republican Sen. Rudy Boschwitz in 1990. Afterward, left-leaning Mother Jones magazine called him "the first 1960s radical elected to the U.S. Senate."

Wellstone pledged to stay for no more than two terms, but last year announced he would be running again. In February, he said he had been diagnosed with a mild form of multiple sclerosis but didn't stop campaigning.

"For me, no stress would be stress," Wellstone said at the time. "The stress of this campaign is what I want to do, to be perfectly honest. And the stress of being a senator is what I want to do."

Wellstone also had two sons, David, 37, and Mark, 30, and six grandchildren. Funeral arrangements were incomplete.

The Associated Press contributed to this report.