A fire at Sen. Bernie Sanders’ Vermont office is being investigated as arson, the Burlington Fire Department said Friday.

Firefighters were dispatched Friday morning to the building that houses the independent senator’s only congressional office in the state. They found “a fire in the vestibule between the elevator and the entrance door to [Sanders’] office,” the fire department said in a news release.

Police in Burlington said “an unknown male subject entered the vestibule” of Sanders’ office…