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

Some $10 million in damage was done as 41 homes burned Monday at the Hunters Brooke (search) subdivision, about 25 miles south of Washington. A dozen of the homes were destroyed.

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.

Investigators confirmed arson caused the fires in at least four homes near Indian Head in Charles County, said Faron Taylor, a deputy state fire marshal.

FBI spokesman Barry Maddox said ecoterrorism was one of the motives that would be investigated.

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.

"We are not going to reveal where in the homes the fires were set, or the method of ignition," Taylor said late Monday. "Only the perps and us know that, and we're not going to tip our hand."

The homes, which were not occupied, were priced between $400,000 and $500,000. The Sierra Club (search) called the development of more than 300 homes "quintessential sprawl" in its Fall 2000 sprawl report, noting it is far from existing infrastructure and "threatens a fragile wetland and important historical sites near the Chesapeake Bay."

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 (search) has also claimed responsibility for fires at lumberyards and sport-utility vehicle dealerships.

The group has caused more than $100 million in damage since 1996, the FBI says.

The Maryland development was not far from the state's Mattawoman Natural Environment Area (search) and Araby Bog (search), one of the state's largest magnolia bogs. The Sierra Club has said the development would severely degrade the bog.

The homes, on lots about a quarter acre each, were spread over a 10-acre area, Taylor said. Television coverage showed the fires, first reported before 5 a.m. Monday, at scattered spots around the neighborhood.

Environmental groups and some county residents sued the Environmental Protection Agency (search) and the Army Corps of Engineers (search) last year, claiming they had violated the Clean Water Act by granting permits that allowed construction at the site.

On July 23, U.S. District Judge Peter Messitte denied a request for an injunction against construction of the development, but ordered the Army Corp to provide a "more complete explanation" of its decision authorizing the sewer line and road in the subdivision. That same day, the Army Corp filed an appeal of that decision.

Patricia Stamper, an Indian Head resident and a plaintiff in the lawsuit, said investigators had not contacted her Monday, and she doubted members any of the groups involved in the lawsuit would have turned to arson.

"I was totally shocked," she said. "I didn't expect it and have no idea what the motive was. Our group certainly had nothing to do with it."

Jacque and Dawn Hightower came to the development Tuesday morning, hoping to see if their house was damaged. They had looked at aerial photos online and thought their home looked OK, but they weren't sure.

"We're left not knowing whether or not we can get into our house," Dawn Hightower said. "It was not an act of God. There's got to be someone who's responsible for this."