The fire that gutted a Brewer bar late Thursday night was set intentionally, investigators believe.

The fire had “an intentional human element,” Sgt. Scott Richardson of the state fire marshal’s office said Monday. “What we do is eliminate all the possibilities and see what is left.”

A Bureau of Alcohol, Tobacco, Firearms and Explosives trained dog found firestarting materials at the scene, “but we have to wait for the laboratory to make that determination official,” he said.

The investigation has focused on the steps leading to the upstairs apartments, where most of the damage is visible.

The fire marshal’s office arrived Friday to investigate the fire.

A woman driving by noticed the fire at around 11:10 p.m. Thursday and stopped to call 911. She ended up helping to guide to safety four people trapped on the roof after flames had engulfed their usual exit.

The four people were in one of two upstairs apartments above Cap’s Tavern and apparently climbed out a window onto the roof to escape. The woman helped get them from roof to roof and onto the ground.

Del Merritt, who owns the South Main Street bar along with Judy’s bar in Bangor and Speedway 95, spent part of Monday with inspectors.

“I don’t know a thing yet,” Merritt said.

Fire investigators continue to work with Brewer Police Department to interview people in the area the night of the blaze.

“We have a lot of work left to do,” Richardson said.

Anyone with information about the blaze is asked to call Brewer Police Department at 989-7001.