FOND DU LAC – Three people died in a Thursday morning fire at a group home for people with cognitive disabilities, authorities confirmed.

Although firefighters had put out the fire, the smell of charred wood still hung in the air around noon Thursday as investigators in white body suits moved in and out of what remained of the house, in the 600 block of South Military Road. The front of the home, once gray, is now black and, in some places, crumbling to ashes.

Fond du Lac Fire/Rescue responded to the home for a report of a fire just after 6 a.m. Thursday.

Paul and Julie Thelen own the home, according to Dyann Benson, Fond du Lac community development director, and county property records. It is rented out for people with cognitive disabilities to live in group setting, Fire/Rescue Chief Peter O'Leary said. As a four-unit home, it wasn't regulated by the city, Benson said. The Wisconsin Department of Health Services doesn't regulate it either, an agency spokeswoman said.

Firefighters found the porch of the two-story home engulfed in "heavy fire, conditions," according to Fond du Lac Fire/Rescue.

Two of the house's five residents were outside with an off-duty State Patrol trooper who was in the area, according to the fire department. The residents got out when a witness ran up to the home and began banging on the door.

The fire was “stubborn,” O’Leary said, adding the blaze traveled to many different spots in the home. The three other adults were found dead inside the home.

Off-duty Fire/Rescue personnel and multiple fire crews responded to the fire, including the town of Fond du Lac, North Fond du Lac, Lamartine, Eden and Ripon, O'Leary said. The American Red Cross also responded to the scene.

The fire is a "truly tragic event," said Liz Morrell, executive director of The Arc of Fond du Lac. The organization assists those with varying abilities to become "independent and integrated into the community," according to its website.

"Everyone here at the Arc Fond du Lac is absolutely devastated and heartbroken," Morrell said. "We offer our sincere condolences for all those involved and all the family members and staff impacted."

When Jeff Faber arrived at W.J. Leasa Electric at 5:45 a.m. Tuesday for work, there were no signs of a fire in the home across the street. Nearly 15 minutes later, his coworker also saw nothing unusual as he started his workday.

About 10 minutes later, however, a person pounded on the window, shouting there was a fire, Faber said. He stepped outside, and the front of the neighboring home “was engulfed in flames,” he said, describing the scene as “pretty dramatic.”

He called 911, although in the distance, he could hear the sirens signaling help was on the way. He stayed until the department put out what to him looked like “the majority of the fire” at the front of the building about 20 minutes later.

Fire/Rescue, Fond du Lac Police and State Fire Marshal Fire investigators are working to determine the cause of the fire. As of 2 p.m., The Fond du Lac County Medical Examiner had taken the victims to conduct autopsies and make positive identification so next of kin can be notified, according to Fond du Lac Fire/Rescue.

“Our members are saddened by the outcome of this morning’s deadly fire” O'Leary said in a statement. "We offer our deepest condolences to the family and friends of those who lost their lives this morning.”

The fire is not the first this year to claim a life in Fond du Lac.

On May 19, Wendy K. Brehmerm, 58, died in a house Woods Place. In June, six people died in a house fire in Langlade County, including an 11-month-old baby, according to USA TODAY NETWORK-Wisconsin archives.

This story will be updated as more information is available.