ELF and the Animal Liberation Front (ALF) have committed more than 600 criminal acts since 1996, causing more than $43 million in damage.

Between 1993 and 2003, the number of special agents dedicated to the FBI's counterterrorism programs grew by 224 percent to 1,669 - nearly 16 percent of all FBI special agents, said James Jarboe, an FBI domestic terrorism expert.

In 1980, disaffected environmentalists formed a radical group called "Earth First!" and staged a series of protests and civil disobedience events, Jarboe said. About 12 years later, the ELF was founded in Brighton, England, by Earth First! members who wanted to use criminal acts as a political tactic.

ELF promotes "monkeywrenching," another word for acts of sabotage and property destruction, against industries perceived to be damaging to the environment.

Jarboe said arson is the most destructive practice of groups like ALF and ELF, which consistently use improvised incendiary devices equipped with crude but effective timing mechanisms.

lrosetta@sltrib.com