LINCOLN – State fire investigators today expect to finish examining the scene of a major fire Sunday that destroyed two Main Street buildings and displaced six businesses.

“It is really necessary for us to finish our examination before we release our findings,” said Sgt. Stewart Jacobs, the state fire investigation supervisor. He said the cause of the downtown fire remained under investigation.

Although state fire officials have not determined the cause of the fire, many residents say they believe it was arson. Sunday’s fire came three days after a fire that destroyed two buildings and displaced four businesses just across the street.

Seven state fire investigators assisted by five agents of the Bureau of Alcohol, Tobacco and Firearms spent much of Tuesday examining the building at 26 through 30 Main St., which was destroyed in Sunday’s fire.

Jacobs said officials were able to confirm that the fire started in the basement of that building.

Before fire officials entered the charred rubble of the building, they assessed its structural integrity to make sure it was safe to enter. Once that process was complete, investigators and agents went in and began conducting a fire scene examination.

“It is a detailed analysis of the fire damage done to the building, an examination of the burn patterns and the fire travel,” said Jacobs. He said the detailed examination confirmed that the fire started in the basement of the building .

Fire officials also began examining the utilities in the building such as heating units and electrical units. Jacobs said each potential ignition source would be independently examined.

JJ, a black Lab fire investigation dog, assisted fire officials. Jacobs said JJ is commonly used at fire scenes to examine the area where the fire started and to screen the site for evidence of the use of accelerants. “It’s a tool we commonly use at fires, and we are fortunate to have her available,” he said.

Jacobs said five federal agents from the Bureau of Alcohol, Tobacco and Firearms provided assistance to state investigators. “The ATF agents provided to us were very valuable in the fire investigation process and allowed the overall investigation to maintain a sense of momentum,” he said. “ATF is routinely considered a valuable asset to the Fire Marshal’s Office, whether it’s fire, criminal or explosion investigations.”

Fire officials along with two Maine State Police detectives continued to conduct dozens of interviews and are following up on information.

“Because of the size of the property and the number of people affected, it has given us a significant number of people to talk to,” said Jacobs. “We have been able to make contact with all of the owners and occupants. We have followed up with people who have come forward with any information. We have talked to firefighters involved in the initial fire suppression efforts. We continue to receive information that needs to be chased out and verified,” he said.

Last Thursday’s fire was determined to have been caused by an overloaded extension cord.

The two major fires in a four-day span have destroyed about 25 percent of Lincoln’s downtown business district, which town officials say could cost more than $1.1 million to replace.

The fires destroyed four buildings, which housed 10 businesses. Those businesses employed about 40 people.

In the meantime, town officials are working on a plan to rebuild the town’s downtown.