Firefighters battle the huge blaze in a warehouse on S. Pickett Street on Sept. 2 in Alexandria. (Bill O'Leary/Washington Post)

The fire that ripped through a 2-story warehouse in Alexandria on Sept. 2 was not accidental, fire marshals have concluded, and a person of interest has been identified in the case.

That person has been interviewed but is not in custody, Alexandria Fire Chief Adam Thiel said at a press conference Tuesday evening. He said authorities are “not concerned” that the person will cause any more harm to the community. He declined to elaborate.

The Bureau of Alcohol, Tobacco, Firearms and Explosives helped the Alexandria Fire Department determine that the fire was incendiary in nature. Officials will not label the fire “arson” because the word “has a specific legal definition,” Thiel said.

“How this case will be prosecuted and what will happen next is up to the Commonwealth’s Attorney,” he said.

More than 200 firefighters fought the blaze, which began shortly before noon last Monday inside a low-slung building at 801 S. Pickett St.

No one was inside the building when the fire started, Chief Fire Marshal Robert Rodriguez said at the time. The roof collapsed as firefighters dealt with the blaze, he said, but they were able to evacuate safely. But four firefighters were hurt, including three from Alexandria. Two remain off duty with minor injuries.

The Alexandria Fire Department estimates the cost of the damage at $6 million.