When fires broke out high on Vail Mountain five years ago, a shadowy group calling itself the Earth Liberation Front quickly took responsibility.
The fires were set Oct. 19, 1998, the group claimed, to protest an expansion project at the famed ski resort.
Work on the controversial project, which has since created Vail's Blue Sky Basin trail network, was set to begin the next day.
Several facilities were lost to the fires, most notably the resort's mountaintop Two Elk Lodge.
In all, the fires caused an estimated $12 million in damage, making the event the most destructive act of ecoterrorism at that time in America, officials said.
Now, five years later and halfway through the statute of limitations for arson, the Vail fires remain an unsolved crime. And they no longer are considered the worst of their kind. This year alone, the ELF has claimed responsibility for arson attacks that caused more than $50 million in destruction in California.
Elsewhere, smaller acts of politically motivated vandalism, arson and animal releases across the country are on the rise.
With the accumulated toll of the attacks now estimated at more than $100 million, environmental extremists have become the top priority for FBI domestic terrorism squads across the country.
But what the agents are pursuing, they have learned, are groups that are not groups at all, but movements with no members, no home offices and no clearly identifiable leaders.
"It makes it very hard to apply the traditional law enforcement methods and techniques that we used successfully against the Mafia, a lot of the street gangs and a lot of drug organizations," said Steve Olson, supervisor of the FBI's domestic terrorism unit in Denver. "There is no leadership per se. It's really more of a philosophy than a traditional organization."
There have been some convictions. But the bigger acts of vandalism, including the Vail fires and the torchings this year of a construction site in San Diego (causing $50 million in damages) and of sport utility vehicles at a car dealership in Southern California seldom leave much useful evidence for investigators.
The perpetrators sneak in, set their fires and then sneak off, generally under the cover of night and always with the understanding that they will never talk about what they just did with anyone else, officials believe.
Olson still has agents investigating the Vail fires full-time, he said. He would not discuss the case but indicated that his squad has not run out of leads.
"If I was an individual who either directly participated in the Vail arson or was a co-conspirator, or had anything to do with that, I would be nervously looking over my shoulder," he said, "because we haven't forgotten, we haven't quit and we haven't given up.
"Are we frustrated that we're five years down the road and haven't solved that case yet? Absolutely. But that frustration serves as a motivator for us."
"Dingo," an environmental activist in his 30s who splits his time between protest communities in Arizona and Northern California, says he grew up in Evergreen and that his real name is Steve Jameson.
In the days after the Vail fires, he traveled to the resort town to help keep alive the ongoing nonviolent protests of the 600-plus-acre Blue Sky Basin expansion.
Many who had been protesting abandoned the cause after the fires, fearful that they might be implicated, he said.
Dingo is his "forest name," he said, the name by which he is known to others involved in so- called "direct action" protests and civil disobedience.
A veteran of Earth First!, a radical environmentalist group founded in the 1980s by conservationists who believed that mainstream groups such as the Sierra Club were failing to affect American environmental policy, Dingo says ELF-style attacks usually are conducted by younger activists.
They believe that even Earth First!, known for taking up the techniques of "monkeywrenching" - spiking trees to stop logging, pulling up survey stakes, pouring sugar into the gas tanks of bulldozers - is too timid, he said.
"Not that I advocate ELF, but I totally understand the people who've had enough of ... being nice to the authorities," he said. "The environment doesn't seem important to most people. I think it's inevitable that things escalate when the other tactics don't work."
He said he does not consider ELF attacks to be terrorism.
But the Vail fires did more than destroy a few buildings. They scared a lot of people, said Bill Jennings, the ski mountain's chief operating officer.
"I don't think there's any way you can look at this and not define it as terrorism," Jennings said. "It is a terrorist act because besides destroying property, it affects people emotionally. It changed our lives. We live in a valley where you don't lock the door to your house, and that was violated five years ago."
Most mainstream environmentalists agree that escalating attacks of ELF and its sister movement, the Animal Liberation Front, are terroristic, said Rocky Smith of Colorado Wild, an environmental group that attempted but failed to stop the Blue Sky Basin expansion by suing in federal court.
"I just reject that thinking. I think it's sick," he said. "You saw it on Sept. 11, 2001, on a grand scale. It's pathological."
Those who are burning down buildings are only hurting the larger cause, he said.
In Vail, the resort company that mainstream environmentalists were trying to portray in their campaigns as a corporate evildoer in 1998 suddenly was seen by the public as a victim, he said.
Although Dingo said he thought extremists should be given credit for not having hurt anybody in 20 years of direct action, he admitted to a charge made by critics, that when and if somebody is hurt in an attack, neither ELF nor ALF will take credit.
FBI investigators and other critics of ELF said they expect the current escalation of activity to continue. Just as Earth First! evolved from the mainstream and ELF emerged from Earth First!, the escalation of tactics may continue, they said.
Eventually, someone will be hurt or killed, probably accidentally the first time but eventually even intentionally, said Ron Arnold, executive vice president of the Center for the Defense of Free Enterprise in Bellevue, Wash., and author of the 1997 book "Ecoterror: The Violent Agenda to Save Nature."
"What happens when the next generation comes along and gets tired that these arsonists, the ecoterrorists, aren't doing (enough)?" he said.