The FBI and ATF are investigating a suspected arson on Camano Island that may have been an act of domestic terrorism known as eco-terrorism.

FBI Agent Robbie Burroughs said firefighters responding to the fire at a home under construction early Tuesday morning found a bed sheet draped across a masonry gate in front of the house. The sheet was spray-painted with a threatening message, which she would not reveal.

“They are here, so I’m concerned,” Sheriff Mike Hawley said, referring to eco-terrorists. He noted that more and more affluent people are moving to the county, particularly South Whidbey, and building giant, custom-built homes.

“We are becoming a target,” he said.

Burroughs said agents won’t be certain the fire was arson for at least a couple of days. Investigators have to wait for the remnants of the fire to cool off before they can analyze the scene and determine the cause of the fire.

The Island County Sheriff’s Office reported that neighbors of the unoccupied home saw flames coming from the second floor and called 911 at about 4 a.m. The three-story structure, reportedly valued at more than $3 million, is under construction on the 900 block of Good Road.

Arson investigators from the Sheriff’s Department responded to the scene of the suspicious fire, but turned it over to the FBI a few hours later.

Burroughs said this may be the first case of eco-terrorism the FBI has investigated in Island County, though there have been similar arson cases in Snohomish County. She said the home was very big, but it wasn’t in an environmentally sensitive area.

Burroughs said the FBI only gets involved in an arson case if it’s suspected of being an act of terrorism.

Acts of eco-terrorism, from arson to vandalism, are usually committed by radical environmentalists as a protest against development. The FBI defines eco-terrorism as the “use or threatened use of violence of a criminal nature against innocent victims or property by an environmentally-oriented, subnational group for environmental-political reasons, or aimed at an audience beyond the target, often of a symbolic nature.”

Hawley said the Island County residents shouldn’t panic, especially since an unoccupied home not far from Interstate 5 was targeted. Yet he said there’s reason to be alert.

“I want to offer a word of warning to someone building a home of this stature,” he said.