PORTLAND (AP) — Hours after a Halloween party, smoking materials that were improperly disposed of caused a fire that killed six people in a Portland apartment — Maine’s worst fire in 40 years, officials said Wednesday.

The fire was an accident that started on the porch before spreading into the home, said Steve McCausland, spokesman for the Maine Department of Public Safety. David Bragdon, the father of one of the victims, said investigators told him they believe the fire started in a cigarette bucket on the porch.

Fire investigators planned to release their full findings later Wednesday morning.

The fire started early on Nov. 1 after a Halloween party the night before. Several partygoers slept over in the apartment house.

It killed Portland residents Nicole Finlay, David Bragdon Jr., Ashley Thomas and Christopher Conlee, Topsham resident Maelisha Jackson and Rockland resident Steven Summers. Several others escaped.

McCausland said smoking materials are typically defined as cigarettes, cigars or pipes. He said he didn’t think investigators were able to determine which it was in this instance.

The deadly blaze led to legal action and to the creation of a task force that met with landlords, tenants and the Portland Housing Authority to come up with recommendations for safety improvements.

The house had a history of code violations. Gregory Nisbet, its owner, didn’t immediately return a call seeking comment.

The federal Bureau of Alcohol, Tobacco, Firearms and Explosives assisted in the investigation, with scientists using a computer model to recreate the conditions of the apartment.