Thousands of people, including firefighters from across the nation and Canada, are expected to attend a public memorial service for Berwick firefighter Capt. Joel Barnes, who was killed Friday while fighting an apartment building fire in Berwick.

The memorial service will be held Sunday at the Cross Insurance Arena in Portland beginning at 11 a.m. A private family Mass will be held Sunday prior to the public ceremony.

Immediately following the services, a procession will go to Calvary Cemetery in South Portland where Barnes will be buried with full fire department honors.

Fire investigators returned to the scene of the fatal Berwick fire on Bell Street on Monday.

State Fire Marshal Joseph E. Thomas said state investigators are working with agents from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives to build a digital model of the building to try to simulate the fire to learn more about how it progressed.

Barnes died while working with a team fighting the fire from inside the building. Firefighters said Barnes was leading another firefighter when conditions suddenly worsened.

Thomas said the cause and origin of the fire have not been identified. Officials believe it started on the top floor of the three-level building.

An autopsy was performed on Barnes on Saturday by the New Hampshire Office of the Chief Medical Examiner, but the cause and manner of his death has not been released.

Crews from 17 communities battled the fire Friday. Four other firefighters were treated for injuries and released from a hospital.

Barnes, 32, was a paramedic and served as the Berwick Fire and Rescue training officer and emergency medical services coordinator. He was a 2005 graduate of Old Orchard Beach High School and previously had worked at the Old Orchard Beach Fire Department.

Barnes’ family is asking that any donations made in his name go to the Berwick Volunteer Firefighters Association, care of Kennebunk Saving Bank, 2 School St., Berwick, Maine 03901.