The cause of a four-alarm fire that destroyed a building under construction at the Mount Auburn Apartments in 2024 cannot be determined, according to an investigation by the Bureau of Alcohol, Tobacco, Firearms and Explosives.

A 15-page report on the investigation was obtained by the Sun Journal through a Freedom of Information Act request.

The fire broke out Sunday night, Sept. 8, 2024, with witnesses reporting flames shooting 30 feet in the air that were seen from nearby towns.

Eleven fire departments responded to the blaze in addition to Auburn, including Lewiston, Turner, Durham, Mechanic Falls, Paris, Oxford, Poland, Minot, Gray, New Gloucester and North Yarmouth.

No one was reported injured in the blaze and the buildings were unoccupied and still under construction.

In addition to the ATF investigators, the Maine State Fire Marshal’s office, the Auburn Fire Department and the Auburn Police Department were involved in the probe, which included a systematic investigation of the fire scene, interviews with site personnel, a review of video surveillance footage and large excavation of the fire scene.

Investigators were able to determine the fire originated in Building No. 2, but could not determine a precise location within it. Building No. 2 was destroyed and has since been rebuilt. It is the building closest to BJ’s Wholesale Club.

Following the fire, speculation arose that a lithium battery or someone trespassing could have started the fire. Both are mentioned in the report, but there was insufficient evidence to support either theory.

The construction site supervisor told investigators there had not been any incidents or threats from former workers, but did say they “had issues with transient individuals trespassing during business and off hours” in the early phases of construction. As a result, fencing was put up around the site.

In surveillance video from the night of the fire, the report said, an individual was seen walking by the construction office trailer, which was on the opposite side of the property at the time. It is currently located adjacent to Building No. 2.

The report states: “The individual walks towards an electrical pole at the front of the property and spends some time bent over in this location. The investigators reasoned that the unknown individual was using a receptacle on the pole to charge some kind of electrical device. The individual then walks away from the construction trailer and towards Building No. 2”

ATF agents inspected the area and found a piece of solid foam with a partial shoe print embedded in it, which was collected as evidence. It is the only piece of evidence connected to the investigation listed in the report.

The construction supervisors also told investigators that a drywall crew had been in the building the weekend of the fire and that one or two doors were left unlocked.

The construction supervisor also relayed to investigators that a few days before the fire, a worker on the upper floors of Building No. 2 had approached a supervisor with a faulty lithium battery that was getting hot to the touch even while not in use.

The supervisor told the worker to get rid of the battery, but it is unknown if the battery was removed from the building, the report states, adding that “this piece of equipment may have been discarded prior to the fire and no such item was found in the debris pile.”

Because the building was still under construction, there was no electrical service or water supply installed at the time of the fire, with no fire protection or suppression systems active in the building.

As previously reported by the Sun Journal, the investigation report acknowledges that Building No. 1 received only superficial damage, with the report referring to “light heat damage on the side that faced Building No. 2, with some melting of the siding but no mass loss and no charring.”

The ATF report describes the damage to Building No. 2 as “catastrophic,” leading to the near complete collapse of the structure. The only remaining walls were at the front of the building, nearest Mount Auburn Avenue, where only the exterior wall structure remained standing.

The use of an accelerant-sniffing canine was ruled out as an investigative tool, because the report states “the fire department had already used an excavator to clear debris, remove unstable structural components, and check for hot spots.”

Investigators used the excavator to comb through the debris pile to look for evidence of “fuel packages” and heat sources, but reported “nothing of significance was identified during this process.”

In the report’s conclusion, the senior special agent and certified fire inspector assigned to the case wrote, “while there was information indicating that a faulty lithium battery may have been present in the building in the days before the fire, no such battery was found during the examination.

“Furthermore, there was an unidentified and unauthorized individual on the property shortly before the fire; however, there was no data to suggest that the individual entered Building No. 2 or was involved in the fire.

“While these pieces of data present viable fire cause scenarios, neither could be effectively ruled out. Therefore, the cause could not be determined to any degree of scientific certainty. The investigators classified the fire as UNDETERMINED.”

The investigation is ongoing.

Within a month, the developer of the complex,  A.R. Building Co., confirmed it would replace the destroyed building, but has never discussed the cost of the fire or any aspect of the investigation.

Building No. 2 is nearing completion and is expected to start leasing apartments this spring or early summer. Tenants began moving into Building No. 1 in June 2025.