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Raleigh officials said they can't determine the cause.
"It's very disappointing. I'd like to know because I'd like to prevent the next one from happening," said Raleigh Fire Chief John McGrath.
WATCH: Update on the downtown Raleigh blaze
Fire officials give update on downtown Raleigh fire
Investigators did find fuel accelerant, but say that's not unusual for a construction site and ABC11 is told a cigarette was definitely not the source.
Officials say the fire could have been an electrical malfunction, intentionally set, or accidental started by a squatter trying to keep warm that cold night.
"We did a thorough chemical analysis below the fire and as much as possible, but it made the investigation extremely difficult because there were no burn patterns because the fire consumed every bit of the wood and turned it into ash," said McGrath.
The fire was the largest Raleigh has seen in nearly a century. A crane at the construction site collapsed as firefighters were arriving on scene and residents were evacuating their apartments.
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The federal government sent resources to Raleigh. ABC11 was there when the ATF rolled its Mobile Command Unit into town and agents dispersed.
MORE: Complete coverage of the downtown Raleigh fire
More than 100 people worked the investigation and they conducted more than 300 interviews.
The city says the federal assistance was helpful.
"If we had done it on our own, we would still be hunting down and doing interviews and leads," McGrath said.
On Friday, around the Metropolitan, there were still several heavily damaged buildings.
Windows are boarded up and there's black tarp hanging outside the Bulla Youth Center on Edenton Street. A construction crew is making repairs.
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Officials says the blaze caused approximately $50 million worth of damage downtown.
The city says moving forward there will be greater oversight on construction companies adding to the Raleigh skyline.
"Every building, no matter what it is, is vulnerable at some point because the life-safety systems are not built in. Unfortunately, this building was at the optimal, at its most vulnerable point when this incident occurred," McGrath said.
The immediate area around the Metropolitan remains closed off. Fencing is up and a security crew is doing rounds.
McGrath says the area was released weeks ago back to the owners and construction company.
The news comes as nearby business owners and residents say work at the downtown site has ceased and they are wondering when all streets will reopen.
RELATED: Residents say no work being done at site of downtown Raleigh fire