The inferno that consumed the Hawaii town of Lahaina last year emerged from the remnants of a brush fire that firefighters had believed they had contained and extinguished, federal investigators concluded in a report released Wednesday.

That determination confirms what has long been suspected about the fire that killed more than 100 people on the island of Maui. Residents have previously described how the flames emerged in the same area where firefighters had spent the morning battling a blaze triggered by downed power lines. Heavy winds rapidly stoked the renewed flames into residential streets, leaving many with little chance to escape.

But until now, local authorities had left open the possibility that there could have been something else that triggered the blaze that swept through Lahaina. Now, in a report released jointly with the Maui County Department of Fire and Public Safety, investigators with the Bureau of Alcohol, Tobacco, Firearms and Explosives concluded along with local investigators that the initial fire had never been fully extinguished — and was able to reignite and spread.

Brad Ventura, Maui’s fire chief, said at a news conference on Wednesday that a rekindled fire is something that nobody wants to see happen. But he said the department was confident in the actions of the firefighters who were on scene that day and had made the decision to depart.

“We stand behind them on their decision,” he said. “It is hard. We will be working with them, but we will be standing by them.”