The final four defendants awaiting trial for conspiring in arsons and sabotage by radical environmental groups took plea deals Thursday in federal court in Eugene, bringing a declaration of victory among law enforcement agencies that worked a decade to dismantle the secretive cell.

In public statements, two of the defendants expressed their regret for crimes they now consider misguided deeds done out of deep devotion to environmental causes.

The four are among 13 defendants in "Operation Backfire," the name investigators gave to their effort to solve a score of arsons over five years in six states that did an estimated $30 million in damage. Most of the arsons were claimed by the shadowy Environmental Liberation Front and Animal Liberation Front.

With Thursday's court action, all defendants have pleaded guilty except three who remain fugitives and are believed to be out of the country.

Under the plea deals, three of the defendants - Daniel Gerard McGowan, 32; Nathan Fraser Block, 25; and Joyanna Zacher, 28 - may get eight-year prison terms. The fourth, Jonathan Christopher Mark Paul, 40, may get a five-year term. All are free to argue for shorter terms at their sentencing hearings, which have not yet been scheduled.

McGowan admitted taking part in 2001 fires at the Superior Lumber Co. in Glendale and at Jefferson Poplar Farm in Clatskanie. Block and Zacher admitted their roles in 2001 in burning 35 vehicles at the former Joe Romania Chevrolet Truck Center in Eugene and in the fire at Jefferson Poplar Farm.

Paul admitted helping to destroy the Cavel West Horse Meatpacking plant in Redmond in 1997.

Thursday's plea deals, unlike the six earlier ones, do not require the defendants to testify against each other or against other co-conspirators - a condition the four defendants demanded in a joint settlement offer made to the government.

Assistant U.S. Attorney Kirk Engdall said the government accepted the no-testimony proposal in order to settle the case. But the defendants' demand carried a price. The government is recommending the four get proportionately longer sentences than the six co-defendants who agreed to cooperate fully, he said.

While the case is all but over, more arrests are possible, Engdall said.

"We believe we have basically disassembled the Northwest cell of ELF/ALF arsonists," Engdall said. "There may be other arrests."

Within moments of the guilty pleas in Eugene, U.S. Attorney Karin Immergut led seven other local, state and federal law-enforcement officials into a press conference in Portland's federal courthouse.

Immergut praised the hard work and cooperation of the FBI; Bureau of Alcohol, Tobacco, Firearms and Explosives; Eugene Police; Lane County sheriff's office; Bureau of Land Management; U.S. Forest Service; Oregon State Police and the state Department of Justice.

"They were relentless, persistent, thorough and dogged," she said. "They got the job done."

Immergut called the four guilty pleas the conclusion of "the largest case of domestic terrorism in United States history," later amending that to say it was the largest case of eco-terrorism.

Environmental activists have criticized the use of the "terrorism" label against perpetrators of property crimes, saying the label unfairly taints the legal efforts of legitimate activist groups and government dissidents. U.S. District Judge Ann Aiken will decide whether to apply harsher sentences under the federal terrorism statute when the defendants are sentenced.

Robert Jordan, the FBI's special agent in charge in Oregon, said the conspirators deserve the punishment awaiting them.

"They spent year after year using violence to try and intimidate you and your government into their twisted way of thinking," Jordan said. "Instead of using reason and logic, they used fire bombs and destruction. Instead of using peaceful, lawful methods, they used fear and threats."

Jordan said investigators continue to search for the fugitive conspirators. They believe Joseph Dibee, 38, is in Syria, where he had relatives. Another fugitive, Josephine Sunshine Overaker, 31, may be in Europe. Rebecca Rubin, 32, may be in her native Canada, Jordan said.

Jordan disputed a reporter's assertion that it took a long time to solve the case. He noted how the cell took extreme measures to avoid leaving behind any DNA or fingerprint evidence. He also noted their deep commitment to secrecy.

During Thursday's hearing, McGowan told Aiken he stopped doing arson after two attacks because he realized it did not create a better world. He apologized for the property loss, disruption and danger he caused to firefighters.

"I hope that you will see that my actions were not those of terrorist, but of a concerned young person who was deeply troubled by the destruction of Oregon's beautiful old-growth forests and the dangers of genetically modified trees," he said.

After the hearing, Alexandra Paul said her brother - defendant Jonathan Paul - immediately recognized arson was wrong after he participated in the Cavel West attack. She recounted his lifelong efforts to fight the fur industry, to free laboratory animals, to thwart whale hunting and to save ancient forests.

"Mr. Paul retains the hope that humans will embrace environmental sustainability and renounce animal cruelty and exploitation," she said. "He intends to continue to pursue those goals in an ethical and transparent way."

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OPERATION BACKFIRE:
The defendants and their deals.
• Stanislas Gregory Meyerhoff - 15 years, eight months.
• Kevin Tubbs - 14 years.
• Chelsea Dawn Gerlach - 10 years.
• Daniel Gerard McGowan - Eight years.
• Nathan Fraser Block - Eight years.
• Joyanna Lynn Zacher - Eight years.
• Suzanne Nicole Savoie - Five years, three months.
• Kendall Tankersley - Four years, three months.
• Jonathan Paul - Four years, two months.
• Darren Todd Thurston - Three years, one month.