ST. AUGUSTINE, Fla. -

Investigators with the Bureau of Alcohol, Tobacco, Firearms and Explosives have joined state and local authorities investigating four separate fires of historic buildings in downtown St. Augustine within blocks of each other before dawn Monday.

By afternoon, St. Augustine police said three of the four fires were arson, and they believe all four may be connected.

Fire investigators release surveillance video of person of interest Surveillance video from the area shows a man investigators believe may have been responsible for at least one of the fires. He is seen wearing what appears to be a white T-shirt.

According to St. Johns County Fire Rescue, the first fire was reported at 3:25 a.m. at the architectural office for Dixon Design Group on 45 Cordova St. When fire crews arrived, flames and smoke were coming out of the building.

Josh Lemaster said he was outside hanging out with some friends when he saw smoke coming out of the building.

IMAGES: 4 fires within 1 mile
LISTEN: 911 calls | Officials' radio traffic
1st PERSON: Fires hit community hard

"Eighty feet in the air," Lemaster said. "We seen it from the fort. Basically that whole place there caught on fire and flames were everywhere, smoke was everywhere. It was crazy. I was the first one here. I called police."

Phillip Chandler also witnessed the fire.

"We thought it was a bonfire because it wasn't a lot of smoke. Then we didn't pay any attention to it and later on saw flames and embers going way into the sky," Chandler said.

The building partially collapsed during the fire, according to firefighters, who were able to extinguish the flames in about 15 minutes.

"It was crazy," Chandler said. "I've seen fires before and I've seen a forest fire, a small one, but nothing this big. I've never seen a house on fire. The stairs in the back started falling back. The flames were huge. But they got in here and got it out quick."

People working inside the St. Augustine Police Department reported hearing explosions around the same time the fires were reported.

Fire Rescue said the building was vacant at the time of the fire. No firefighters were injured in that fire.

Investigators said the fire was the result of arson.

A second fire was reported at 3:28 a.m. at an empty home two blocks from the office fire on 17 Saragossa St.

Fire crews saw flames coming from the home when they arrived. They quickly extinguished the fire and no injuries were reported.

Investigators said they have ruled that fire arson. They said the fire was started on the outside of the home with combustible materials.

"It was under the house," St. Augustine Fire Marshal Capt. Bob Growick said. "It wasn't that windy. Unless wind is flowing through there, it's actually going to accelerate the fire. And it was a small fire and it was just starting when the police department actually saw it. Because they started to look at all abandoned homes or the homes that are being used, and the police officer saw it and then we went ahead and secured the scene."

FIRE MARSHAL: 4 St. Augustine fires suspicious About an hour later, around 4:40 a.m., a third fire was reported a few blocks away at a home at 91 Park Place in the Lincolnville neighborhood.