The Chicago Police Department Bomb & Arson Unit’s investigation of the October 26 fire at the Statistics and Mathematics building determined that the fire was accidental, thought it did not rule out negligence as a possible cause.

Though the investigation was inconclusive, the case was shut due to its accidental and non-criminal nature, according to documents filed the next day by the Chicago Police Department (CPD).

The fire started at the first floor entrance doorway, the report reads.

According to detective Dean Graves, a fire official said construction workers had been welding earlier that day at the southwest entrance inside the doorway.

The official speculated that “a possible ember spark got inside the wood and smoldered until a flame developed,” according to the report, and then “fire caught onto the middle staircase and moved upward to the second/third floors venting through the roof.”

The released documents also provide more details on the minor injuries sustained by firefighter Mark Managan, who was taken to the University of Chicago Medical Center’s emergency room. Managan “suffered trauma to head, neck and shoulders from a portion of the construction chain link fence being blown by the gusting wind onto his head,” the report reads. Managan was subsequently discharged from the hospital in stable condition.

The construction on the building stemmed from renovations to create a space for its future role as the Stevanovich Center for Financial Mathematics. The work has been ongoing since last summer and has since resumed progress.

The continued construction also hindered the investigation, according to the report.

Graves’ “was unable to gain access to the structure to conduct an origin and cause investigation due to a chain link construction fence surrounding and securing the building,” according to his report.

The investigation was ultimately closed without conclusive results.

“The [reporting detective] was unable to rule out careless workmen welding on the first floor causing an ember to lodge into the wooden framework and smolder. Based on the above investigation, the [reporting detective] believes this to be an accidental fire and recommend[s] this case be closed non-criminal,” the report reads.