The ruins of a Mission building that was the site of a deadly fire in January, 2015 caught aflame again late Sunday night, in a blaze investigators are blaming on squatters in the crumbling structure.

According to the San Francisco Fire Department's Twitter account, the fire in the vacant structure at 22nd and Mission Streets was reported at 11:22 Sunday evening, and was almost immediately termed at a three-alarm blaze.

Within 15 minutes, inhabitants of neighboring buildings, including the upscale Vida condos next door, were evacuated, and SFFD was searching the abandoned structure at 3222 22nd Street for any rogue inhabitants.

By 12:14 a.m. Monday, a large crowd had gathered to watch the blaze, despite SFFD's requests that people avoid the area.

By 12:26 a.m., the fire was contained. SFPD remained on scene overnight to ensure the blaze did not reignite.

Though no one was injured or displaced in the fire, eyebrows are still being raised at the timing of the blaze, as the building as at the center of a new controversy, after SF's Department of Building Inspection posted an emergency notice on the structure last month, ordering owners to demolish what was left of the building.

The demolition order raised worries that the 60 tenants displaced in the blaze might lose the right to return to their rent controlled apartments if and when the building is rebuilt.

Addressing the media early Monday, SFFD Division Chief Kirk Richardson said that “My belief is that squatters were in there and that they caused the heat source," Mission Local reports.

According to Mission Local, "neighbors have reported taggers going onto the roof via the fire escape and scaffolding that surrounds the building. Others said they’ve seen squatters in the derelict site in the past."

"We had a hard time getting into the building because all the doors were boarded up and the windows were boarded up from the previous fire so we had to cut our way in. The stairwell was filled with debris so we couldn't make it through the interior stairwell so we had to climb the fire escape," Richardson told ABC 7.

Mission Local reports that investigators believe that "the fire originated in the leftmost room on the third floor and that it was possibly caused by cooking," with one saying that a hole cut out of a plywood board covering that room's window was “consistent with homeless living.”