Baltimore fire investigators don’t know what caused the five-alarm fire that burned down the historic city-owned Superblock, with the once-vacant structures deemed to be too unsafe to inspect before they were torn down, documents show.

The cause of the fire has been classified as undetermined, according to an incident report updated Sept. 22.

The fire broke out on Sept. 2, just before 3 p.m., with a witness reporting he saw flames on the rear roof of a building in the 200 block of West Fayette Street, the report said. The witness told investigators he did not see anyone enter or exit the building.

The blaze spread to other buildings on the adjoining 100 block of North Howard Street. The report blamed the conflagration’s expansion on the buildings’ proximity as well as airborne embers and poor-quality roofing, the report says.

Investigators wrote that they could not rule out possibilities that the fire was caused by homeless activity, sparked by improperly discarded smoking materials, or intentionally set.

Light rail service was suspended for three weeks while crews demolished the buildings. Department of Community and Housing Development told The Baltimore Brew that officials tried to salvage some historic buildings, including the New Pickwick theater, but determined that the damage was too extensive.

Tammy Hawley, a housing spokeswoman, said Friday that no additional structures will be torn down beyond those that have already been razed.

She said crews are continuing to clear debris from the site. The most time-consuming aspect of the work was removing the cast-iron facade from 121 N. Howard St., with workers having to drill out the bolts and remove the facade piece by piece.

The former shopping and commercial district, a regional draw that once contained vibrant department stores and retailers, is made up of more than two dozen city-owned parcels across two blocks. It is bounded by West Lexington Street, Park Avenue, North Howard Street and West Fayette Street.

Development rights for the district have been awarded to several teams since a planned reinvestment initiative kicked off in 2003, but the developers have never found the financing necessary for a full rebuild. That’s left the structures vacant over time and subject to decay.

Members of the Baltimore Development Corp., the city’s development arm, which has attempted to match the Superblock with the right developers, raised concerns with Mayor Brandon Scott’s office about the parcel’s condition last December, according to a memo reviewed by The Banner.

The memo called on the city to “successfully redevelop” the Superblock, which was almost entirely abandoned and deteriorating.

Agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives participated in the investigation of the Sept. 2 fire, but a spokeswoman said earlier this week that the city was taking the lead in the investigation.