Fire officials are not sure what caused Monday's blaze at the Sampson family compound in Petaluma, but they're calling it suspicious.

Some people reported hearing an explosion when they called in the fire, which destroyed a mobile home at the sprawling residential property on Liberty Road.

"There are definitely some questions we'd like to have answered," Rancho Adobe Battalion Chief Herb Wandell said.

The fire spread very quickly, which indicates it may have been set intentionally, he said. Also, the building had no power or gas connection, so an accidental fire is unlikely, he said.

It's hard to determine an origin or cause because much of the trailer was destroyed, Wandell said, but there was nothing to indicate an explosion.

Rancho Adobe firefighters received the call at 7:43 p.m., and the building was engulfed in flames when they arrived about seven minutes later, he said.

The closest Rancho Adobe fire station, about 1.5 miles away, was closed that day because of the department's ongoing budget shortfall.

The fire is one of several at the compound that Rancho Adobe firefighters have responded to over the years, Wandell said. Most of the others have been debris fires.

"It's been a problem area," Wandell said.

The Sampson family has had numerous run-ins with neighbors and Sonoma County authorities over the decades, including code-enforcement issues, arrests and political battles.

Homeless people come and go from the residence, sometimes staying in the campers, Wandell said. He doesn't know if a homeless person was staying in the mobile home when it went up in flames.

Nobody was injured in the fire.

Rose Sampson said one of her sons lived in the mobile home until he died three years ago. Nobody has lived in the trailer since then, to her knowledge.

She said she is bedridden, can't leave her home on the property and doesn't know how the fire started.

Fire officials still are interviewing witnesses in an attempt to learn what caused the blaze, Wandell said.