Federal investigators are offering a $5,000 reward for information on a man believed to have fire-bombed a government building in Wisconsin after daylong protests near the State Capitol turned violent Tuesday night.

Protesters toppled two statues, vandalized buildings and are accused of assaulting a Democratic state senator on video at the State Capitol in Madison as chaos erupted in the city.

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Police said a Molotov cocktail was thrown into the City County Building in downtown. The building houses the 911 communications office, Madison Police Department, and other city and county government services.

The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) is asking for the public’s help in identifying a man seen tossing an incendiary device into the government building around 1 a.m.

Investigators are offering a $5,000 reward for information on the individual seen fire-bombing a government building. (Bureau of Alcohol, Tobacco, Firearms and Explosives)

"We are looking to the public to help us identify this individual," Assistant Special Agent in Charge Jon Ortiz, of the ATF St. Paul Field Division, said in a statement. "This is a serious crime that put a number of lives at risk. Acts like this will not be tolerated.”

One surveillance image from the scene shows a man appearing to douse the outside of the building with a substance. A second image shows him holding an incendiary device as it is lit up in flames.

The City County Building in downtown Madison houses the 911 communications office, Madison Police Department and other city and county government services.  (Bureau of Alcohol, Tobacco, Firearms and Explosives)

The violence began after a group of 200 to 300 protesters marched through downtown Madison and escalated once they reached the Capitol grounds. Some tried breaking into the Capitol building, but were repelled by police inside with pepper spray.

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Democratic state Sen. Tim Carpenter, D-Milwaukee, was walking to the Capitol building when he encountered protesters and began recording them. Carpenter said he was “assaulted and beat up” by eight to 10 people as he took the video.

Protesters also turned their anger toward two statues – one of Civil War Col. Hans Christian Heg, who fought for the Union side and was an ardent abolitionist, and one of Wisconsin's motto, "Forward."

Gov. Tony Evers condemned the violence and activated the National Guard on Wednesday. He said there was “significant damage to state property.”

Madison Mayor Satya Rhodes-Conway also condemned the overnight violence, saying it was “incredibly dangerous” and those involved in criminal behavior “will be held accountable.”

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ATF is working with Madison police and fire departments on the investigation. The agency asked anyone with information on the individual to contact the Madison Area Crime Stoppers at (608) 266-6014 or online at www.P3Tips.com.

Fox News' Louis Casiano contributed to this report.