The fire that killed four members of the Sullivan family May 1—and left a single survivor—started with the disposal of ash onto mulch outside the house, police said.
Several officials announced the news at a press conference around 4 p.m. Thursday. They said that Thomas Sullivan, Jr., 20, fully cooperated with the investgiation, and that he told authorities he had smoked cigarettes in that area several times that night.
He was the only member of the family who smoked, according to Carmel Police Chief Mike Johnson.
Dan Tompkins, captain of the Putnam County Fire Investigation Team, called the blaze "the perfect storm," because of strong winds, a stint of recent dry weather and cigarette ash that had been sitting on the mulch for several hours.
Investigators could not say whether smoke detectors sounded.