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Sen. Bernie Sanders addresses Unite Here Local 11 workers protesting outside of Figueroa Hotel in downtown Los Angeles on Friday. Authorities are investigating a blaze that was set at his Burlington, Vt., office that same day.

Damian Dovarganes/AP

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Damian Dovarganes/AP

Sen. Bernie Sanders addresses Unite Here Local 11 workers protesting outside of Figueroa Hotel in downtown Los Angeles on Friday. Authorities are investigating a blaze that was set at his Burlington, Vt., office that same day.

Damian Dovarganes/AP

A fire broke out at Sen. Bernie Sanders’ office in Burlington, Vt., on Friday, damaging the building but leaving occupants unharmed. Authorities in the state now say they are investigating it as arson and searching for an unidentified male suspect.

The Burlington Fire Department said crews arrived at the Church Street office on Friday morning to find the sprinkler system and fire alarms activated, and a “fire in the vestibule between the elevator and the entrance door to Senator Bernard Sanders’ office.”

“The fire was extinguished, and the Senator’s office and surrounding offices were searched and cleared of occupants,” they added.

While no injuries were reported, authorities said the door to Sanders’ office sustained moderate fire damage, and the third floor and floors below sustained significant water damage.

The brick building is home to several office and retail spaces. It formerly housed a Masonic temple and is listed on the National Register of Historic Places, according to local alt-weekly newspaper Seven Days.

The fire department said later in the day that the fire marshal’s office had deemed the fire “incendiary in nature,” meaning it was set intentionally. The Vermont State Police and Burlington Police Department have taken on a joint investigation into the fire’s origins.

Burlington police say they are looking for an unknown male suspect, who sprayed a possible accelerant on the office door, set it on fire and fled the scene, according to The Associated Press.

“A significant fire engulfed the door and part of the vestibule, impeding the egress of staff members who were working in the office and endangering their lives,” police said in a statement. “The sprinkler system then engaged and largely extinguished the fire.”

Authorities have not determined a motive, and say the suspect remains at large. Police released a grainy photo of a man wearing an orange beanie, dark jacket, white Nike sneakers and what appears to be a tote bag.

Sanders, who lives in Burlington and served as its mayor before being elected to Congress, was not in his office or even in the state at the time of the incident. He was rallying with striking hotel workers on the picket line in Los Angeles.

“We are relieved that no one on our staff and, to our understanding, no one in the building was harmed,” Sanders’ state director Kathryn Van Haste said in a statement to media outlets.

She credited the quick work of local first responders, whom she said are now coordinating with U.S. Capitol Police and the Senate Sergeant at Arms.

U.S. Capitol Police protect Congressional buildings as well as members of Congress, both in Washington, D.C., and their home districts.

It said in January that threats against lawmakers had climbed last year, with its threat assessment section opening investigations into 8,008 cases. That’s about 500 more than it saw in 2022, but still lower than the preceding two years.