"We don't live in a country where it's okay to kill people if we don't necessarily. Like what they're doing. If we have someone who actively embraces this then what's next?" says John Lewis.
What's next, he says, is the emergence of a "lone wolf" like Eric Rudolph or Ted Kaczynski, something that has already happened.
A mysterious bomber was caught on surveillance camera in 2003 planting two sophisticated explosive devices late at night outside a company that makes vaccines in northern California, a company targeted by animal rights activists. One bomb was set to go off an hour after the first - after firemen and police arrived – but it was spotted by a night watchman. A few weeks later a third bomb went off outside another company, this one strapped with nails.
"Anyone from 50 feet of that particular bomb probably would have been killed or seriously injured," says the FBI's David Strange, who is in charge of the investigation.
Strange thinks the second explosive was designed to hurt or kill the first responders that show up to the scene. He says it was the first time he heard of eco-terrorists using bombs.
Strange says the FBI has identified the suspected bomber as Daniel Andreas San Diego, a 27-year-old animal rights activist from San Rafael, California, who is now a fugitive after he slipped an FBI surveillance team.
But he left behind a message, posted on a Web site sympathetic to the Animal Liberation Front. Part of it reads, "We will now be doubling the size of every device we make."
"I'll ask you. Why does someone build an improvised explosive device with shrapnel, nails and such, if they're not intending to cause someone grievous harm if not worse?" says Lewis.
There is a definite split in the movement when it comes to violence.
After torching a forest research station in Irvine, Pennsylvania, one ELF cell threatened to "pick up the gun."
"I think it's sort off disingenuous to say 'Well, we can burn down buildings. But we can't use explosives. Or we can use explosives. But we can't do anything that might harm a person.' I think what we have to do is look at the big picture. We have to look at what works," says Dr. Jerry Vlasak.
Since our report first aired last fall, the FBI announced the arrests of 11 people, saying they were part of a criminal group that called themselves "The Family." They're accused of committing over a dozen arsons and other acts of sabotage nationwide, including those fires on top of Vail Mountain.
By Graham Messick