Investigators combed through the rubble of dozens of torched houses Tuesday looking for more evidence of arson in a posh subdivision under construction near a nature preserve. The FBI said it would look into ecoterrorism as a possible motive.

Environmental and community groups tried to block the development in a lawsuit last year that claimed it would hurt one of the nation’s last undisturbed magnolia bogs.

More than 20 federal, local and state investigators searched for forensic evidence Tuesday, Taylor said. He refused to say what led investigators to conclude it was arson.

The Sierra Club issued a statement Monday saying it “strongly condemns all acts of violence in the name of the environment.”

In recent years, radical environmentalists have set fires at luxury housing developments under construction in San Diego and Detroit’s outer suburbs and at a resort in Vail, Colo. The Earth Liberation Front has also claimed responsibility for fires at lumberyards and sport-utility vehicle dealerships.