Seattle -- The attacks have been nearly forgotten. The places that were burned have been rebuilt or relocated. The cryptic communiqués taking responsibility are distant history.
But on Thursday, after years of investigation, federal officials announced one of the biggest roundups yet of people involved in a string of ecoterrorist attacks in the Pacific Northwest dating to 1998.
Six people from five states, from New York to Washington, were arrested on Wednesday, and indicted on charges related to arson attacks and sabotage in Washington and Oregon, including the millennium eve destruction of a transmission tower owned by the Bonneville Power Administration.
The arrests are intended to strike a blow against two related groups, the Earth Liberation Front and the Animal Liberation Front, which have claimed responsibility for burning and bombing research facilities, timber operations and sport-utility vehicle dealers, among other targets.
Both groups maintain Web sites where they discuss operating as independent cells and share letters from colleagues in prison.
"The Animal Liberation Front carries out direct action against animal abuse in the form of releasing animals and causing financial loss to animal exploiters, usually through the damage and destruction of property," the group says on its Web site.
Some of the targets of those attacks expressed relief on Thursday, saying the arrests helped to close out a long period of uncertainty and fear.
"I'm gratified that that the F.B.I. has been diligent in their pursuit of these people," said Steve Swanson, president of family-owned timber company, Superior Lumber, in Glendale, Ore. The veneer and plywood plant was set on fire on Jan. 2, 2001, and the blaze caused about $500,000 in damage, Mr. Swanson said. The Earth Liberation Front took responsibility for the attack.
No one was injured in any of the attacks, but they used sophisticated fire-bombing techniques, officials said. The fires happened from 1998 to 2001.
"If left unchecked these are the kind of crimes that could really hurt someone," Mr. Swanson said.
The attacks have diminished in the Pacific Northwest of late, but they continue in California and the Rockies, where groups have targeted things like ski lifts and condominiums.
"Hopefully these arrests strike a deterrent blow, making these groups realize that the F.B.I. will come after them no matter how long it takes," said Gary Perlstein, a professor of criminology at Portland State University, who tracks ecoterrorism groups.
But Professor Perlstein said the arrests, coming after years of investigation, showed how long it took to bring domestic terrorists to justice.
Federal officials offered little on the arrests or indictments, beyond identifying those who were charged, most of them in their late 20's or 30's, and saying what the crimes were. But they touted the coordinated roundup as one of the biggest in the fight against ecoterrorism.
"This is a significant step in the government's effort to solve these crimes and to get at the activities of the E.L.F. and the A.L.F.," said Emily Langlie, a spokeswoman for the United States attorney's office in Seattle.
Although ecoterrorist groups have tried to maintain independence, Ms. Langlie said the six people arrested "were all associates, and may have been involved with each other."
The arrests did not resolve one of the biggest ecocrimes in the Northwest, the 2001 fire at a University of Washington genetics research laboratory.
The fire fit the pattern of others, in which companies, universities or government agencies that carried out different types plant or animal research were the targets.
Animal and environmental sabotage groups pose the nation's top domestic terror threat, F.B.I. officials told a Senate committee earlier this year. The federal officials said they had 150 open investigations of 1,200 crimes from 1990 to 2004 in which ecosaboteurs had taken responsibility.
The F.B.I. identified both the Animal Liberation Front and the Earth Liberation Front as two groups that were "way out front" on different crimes.
"We have seen an escalation in violent rhetoric and tactics," John Lewis, the bureau's director of counterterrorism, said in his Senate testimony. "Attacks are also growing in frequency and size."
The arrests Wednesday were made in Charlottesville, Va., where a college student, Stanislas G. Meyerhoff, 28, was picked up, and in New York, where Daniel G. McGowan, 31, was arrested. They were indicted by a grand jury in Oregon for the arson at Superior Lumber and the May 21, 2001, fire at the Jefferson Poplar Farm in Oregon.
A 1998 fire at a government animal and plant health inspection site in Olympia, Wash., was the basis of indictments against Kevin M. Tubbs, 36, who was arrested in Oregon, and William C. Rodgers, 40, who was arrested in Arizona. Both men were indicted in Seattle.
Also in Arizona, Sarah K. Harvey, 28, a student at Northern Arizona University, was arrested and charged in connection with a 1998 arson at U.S. Forest Industries in Medford, Ore.
Chelsea D. Gerlach, 28, of Portland, Ore., was charged with two counts related to a crime that got a lot of attention during heightened terrorism fears on the eve of the millennium - the December 1999 destruction of a transmission tower near Bend, Ore.