The arrest of six activists comes as Congress considers increased penalties. But acts of intimidation are also rising.
The arrest of six animal rights activists and environmental radicals last week is the clearest sign in years that law-enforcement authorities now are able to infiltrate the shadowy world of "ecoterrorism."
But the apprehension of four men and two women in five states around the country - all charged with firebombings and other criminal acts committed years ago in the Pacific Northwest - also indicates how hard it is to do that.
While the arrests are significant, many more crimes carried out in the name of protecting animals and the environment remain unsolved. The FBI reports 1,200 such incidents in recent years, ranging from vandalism and the freeing of lab rats to the torching of housing developments and auto dealerships that sell sport utility vehicles. Property damage has totaled more than $200 million, according to members of Congress sponsoring legislation intended to hamper the trend.
Groups such as the Animal Liberation Front (ALF) and the Earth Liberation Front (ELF) usually claim credit for such acts. But as far as law-enforcement officials can tell, there is little organization or structure to the groups. Attackers act alone or in small numbers, adhere to strict security measures in communications and operations, and make use of accessible, unsophisticated equipment like cheap timers.
"Preventing such criminal activity has become increasingly difficult, in large part because extremists in these movements are very knowledgeable about the letter of the law and the limits of law enforcement," said John Lewis, a counterterrorism FBI official, at a congressional hearing. "Moreover, they are highly autonomous."