BUFFALO, N.Y. — Authorities say the fire that broke out at the Buffalo Grand Hotel last Thursday is now being investigated as arson.

Buffalo Fire Commissioner William Renaldo says officials couldn't tell it was an incendiary fire at first.

"We don't try to pre-determine if it's arson, or not an arson,” Renaldo said. “We just let the investigation continue on its natural course and gather evidence, process the scene and take it from there.”

Renaldo says there were about 40 to 50 guests staying at the hotel at the time of the fire, along with a small number of hotel staff. He says there is no person of interest in the case at this time.

Flames ripped through the hotel's ballroom and the kitchen at around 1 a.m.

Renaldo says the local office of the Federal Bureau of Alcohol, Tobacco, Firearms and Explosives is also investigating the fire, because a firefighter was moderately injured from a fall and because dozens of guests could have been hurt.

"They frequently help us out in cases like this,” Renaldo said. “And they've been great, they've always been great. And the next steps is one again, working jointly with the Buffalo Fire Department fire investigation unit, [and] conducting joint witness interviews.”

The blaze broke out just hours after owner Harry Stinson signed a contract with Wyndham Hotels while he was in Canada, where he lives. Stinson said last week that the timing was suspicious, especially since nobody should have been in the area that the fire is believed to have started.

"The interaction between the owner and the contractor, that will come into play," Renaldo said. "A number of people will be interviewed during this process."

The hotel is currently closed; a choice made by the owner. Renaldo says the investigation is ongoing, but cases of this sort can take months. Stinson says he is unsurprised that fire officials determined the cause to be arson.

“What was done here was just so foolish for the danger to people,” Stinson said in a statement. “You have to question what was the upside here."