CLEVELAND, BRADLEY COUNTY, TN (WRCB) – The search is underway for clues into what started Cleveland's largest fire this year.

A three-story, quarter-mllion square foot building, is now, nothing more than a shell.

One thing officials couldn't answer, last week, was anyone inside?

They had several reasons to ask: given how big the building was, how quickly it burned, and how tempting it was for squatters.

It's why they brought in the medical examiner, and the dogs.

"It was a defensive fire because it was so big," says Lt. Donnie Sullivan, arson investigator for the Cleveland Fire Department.

But firefighters would stay another ten hours after the smoke and flames had gutted Jackson Catnapper's old Cleveland Chair Company last Thursday.

"Second, third floors was wood," Lt. Sullivan says. "Wood floor on top of wood floor, so that's where most of the fire came from."

It still smolders five days later.

So do the questions.

"We closed the factory back in 2006," owner Ron Jackson tells Eyewitness News. "It had no electrical service or gas."

But that doesn't mean it was empty.

"It is a frequent place for homeless people to sleep," Lt. Sullivan says. "We're just trying to cover our bases, make sure we don't leave nobody out there laying in the ash."

By late Tuesday morning, 'Rad' is here to put fears and rumors to rest.

The Roane County Sheriff's Belgian Malinois is the first of three cadaver dogs to search the factory's burned-out shell for human remains.

"Once they're through, then we'll let the arson dog come in, let him do his job," Lt Sullivan says.

If not by vagrants, or vandals, how the fire started is the mystery.

Lt. Sullivan says investigators believe they already know where it began.

"It's probably gonna be on the north side, one of two sections on ninth street, that we're concentrating on," says Lt. Sullivan.

Jackson tells Eyewitness News that his family had attracted some interest in the factory property.

But it hadn't received any offers.

"We have a major presence, more than 700 workers manufacturing recliners in Cleveland and Bradley County," Jackson says.

Prior to the fire, the plan was to de-construct, rather than demolish, the 250,000 square foot factory.

"We were hoping to salvage the bricks and save the history," Jackson says.

Until investigators complete their tasks, it's not clear whether salvage would be possible. But even in ruins, the shell yields a legacy; as an open classroom for the firefighters who tried to save it.

"Probably sixty percent of our firefighters are young," Lt. Sullivan says. "They've never seen anything like this at all. They were just really amazed."

At last report, the cadaver dogs had not hit on anything.

Investigators have called the cherry picker and set up roadblocks--to try to keep the scene clear.

They likely will be out again Wednesday.