ROBBINSTON, Maine — Fire investigators have determined that a burning cigarette likely caused the blaze in Washington County that killed an elderly woman and her son earlier this week.

Virginia Carlow, 92, and her son Robert Carlow, 71, died Monday night in a fire that heavily damaged their home on Ridge Road in Robbinston. After an investigation, Sgt. Tim York with the fire marshal’s office determined that the fire started in the living room near a chair where Virginia Carlow frequently smoked. The report attributed the fire to “careless disposal of smoking materials.”

“It was either ash or a dropped cigarette that started the chair,” Steve McCausland, spokesman for the Maine Department of Public Safety, said Wednesday afternoon. McCausland said the investigation has been concluded.

Carlow and her son both lived in the home. Robert Merrill, Robbinston’s fire chief, said Tuesday that an automated alert system prompted a phone call to the Washington County Regional Communications Center in Machias. By the time firefighters arrived several minutes later, there was already heavy heat and smoke coming from the house, Merrill said.

A graveside service will be held for the Carlows at 1 p.m. on Saturday at Brewer Cemetery in Robbinston, according to an obituary notice.