Investigators think the fire was set, but the question remains as to whether it was intentional.
"Open flame ignition from available combustibles" is the formal term from the Office of Fire Investigations. That could mean that someone set the fire. It may also mean that there were squatters inside the building that started the fire to stay warm and it simply got out of control.
Bomb and Arson of the Police Department will continue its investigation, as the historic building comes down.
It is a stubborn fire. Even as the demolition crews work, the flames find life, but not with enough strength to spread again.
Before the demolition began, the Office of Fire Investigations was able to determine through available evidence and witness statements, that the massive fire quite likely was started by human hands.
The Police Departments Arson Bureau will now investigate and in the meantime, the demolition will go on.
The five-story building, which was once home to the Pullman Couch Company had been vacant for years.
It was owned by Chicago developer Calvin Boender, who is currently in prison after being convicted in a bribery scheme that involved West Side Alderman Ike Carrothers. He, too, went to prison.
Three years ago, the city threatened to have the building demolished, but Boender's firm complied with city paperwork and it was allowed to stand until Tuesday night's spectacular fire brought about its end.
The empty warehouse was once part of what was called the Central Manufacturing District, which thrived for decades.
"To see a fire of this magnitude, the aftermath of a fire like this is interesting, but also, to document slowly, but vanishing pieces of the central manufacturing district, this sort of sprawling campus of buildings that this building was once a part of," said architecture expert Lee Bey.
It may take a week bring it all down which does not make poultry vendor Frank Tam across the street very happy.
"The police told me, they said it will probably take a week, or a week and a half, and all that time you'll lose business," Tam said.
The company Boender was associated with has hired the demolition team, so they are paying for the building to be knocked down, not the tax payers.