Investigators believe a fire sparked inside Toronto's Old City Hall on Monday night was deliberately set.

A surveillance camera image of a suspect wanted in connection with the arson investigation was released to the media on Tuesday afternoon.

Firefighters were first alerted to the blaze at around 8 p.m. after the historic building’s sprinkler system went off. Police say that a man broke into the building and set three separate fires within an office on the main floor.

Though the fire was quickly brought under control, investigators with the Ontario Fire Marshal and Toronto Fire Services stayed on scene for hours investigating the cause.

In a news conference Tuesday afternoon, Division Chief Larry Cocco said there was “nothing complicated” about the arson.

“Combustible papers were ignited,” he said. “The actual means are part of the investigation.”

Toronto Police Association President Mike McCormack said that it took police officers two hours to get to the Old City Hall because they were tied up with other calls.

“We are seeing this across the city in every division where the response times are being impacted by the lack of staffing and that is something we have been very concerned about,” McCormack told CP24. “The reality of policing in Toronto is that we don’t have the personnel that we needed.”

Initially, officials would only describe the one-alarm blaze as “suspicious in nature.”

Pegg told CP24 on Tuesday morning that the investigation has since been turned over to Toronto police.

“We can confirm that the fire was intentionally set,” he said.

“The actual scene investigation wrapped up at around 4:30 a.m. The Office of the Fire Marshal and a provincial fire investigator were deployed here overnight and worked with our investigations team (and) with Toronto Police through the night.”

Pegg said the southeast corner of the building sustained smoke and water damage but was otherwise deemed structurally intact.

The cost of the damage is estimated at about $100,000. Some documents were damaged in the blaze but a spokesperson for the Ministry of the Attorney General said none of the affected paperwork relates to criminal cases.

“The fire at Old City Hall impacted the Provincial Offences Act appeals office. Fire and water damage is currently being assessed,” a spokesperson told CP24 via email. “The POA appeals office and matters scheduled in one courtroom have been moved within the building.”

A CTV News Toronto reporter who went inside the building said the damage is limited to an office area inside the building. Media is prevented from taking photo or video inside the building as it is an operational courthouse.

No injuries were reported.

“We are very fortunate that that this building has sprinklers and that the system worked as designed,” Pegg said. “It would have been a much different scenario had that not been the case.”

The building is open today while the investigation continues.