A massive fire last year that tore through two five-story apartment buildings and several bars near Third and Chestnut Streets in Old City was set, officials have determined.

After a nearly yearlong analysis of information from the fire scene, witness statements, and other evidence, the Bureau of Alcohol, Tobacco, Firearms, and Explosives has deemed the blaze “incendiary in nature," according to a Friday statement from the bureau.

The specific cause is still under investigation, an ATF spokesperson said. No suspects have been publicly identified, and the spokesperson did not have details about the next steps in the probe. The Philadelphia Fire Marshal’s Office and the Police and Fire Departments are also involved in the investigation.

The four-alarm fire ravaged the multipurpose building at 239 Chestnut St. and one at 237 Chestnut. It began around 3 a.m. on Feb. 18, 2018, spreading to neighboring buildings and displacing around 150 people and a dozen pets. It took firefighters more than nine hours to place it under control.

The building was quickly declared a “total loss” by the Department of Licenses and Inspections, and the majority of the 166-year-old building — save a cast-iron facade on the first floor — was demolished.

Though the flames were contained to several buildings on the street, businesses on the entire block between Second and Third Streets felt the burn from the fire. The block — which includes a vape shop, apartments, bars and restaurants, and a Best Western hotel — was closed for months during the investigation, putting strain on the tourist-dependent shops shrouded in caution tape and metal barriers.

Capofitto, once home of National Geographic’s No. 1 gelato in the world, officially closed at 233 Chestnut in December, after its owners said the business lost following the blaze was too steep to recover from.