William Spengler Jr. left a suicide note but no discernible motive for why he apparently torched his Webster, N.Y., house on Christmas Eve, luring firefighters to the scene, where he shot and killed two firefighters before killing himself.
Officials said a body found in the rubble has not been identified, but is believed to his sister, Cheryl Spengler, the New York Daily News reported Sunday.
Realtor Laura LaManna told the Daily News Cheryl Spengler had closed on a home in nearby Henrietta and was preparing to sell the Webster home where the siblings were raised.
LaManna said the situation between William Spengler, 62, and his sister was tense after their mother died in October.
"They didn't get along at all, and that's why [Cheryl Spengler] was moving," LaManna said.
A funeral Monday for one of the firefighters, 19-year-old Tomasz Kaczowka, was expected to draw thousands of mourners, the Rochester (N.Y.) Democrat and Chronicle reported. Thousands from across the country attended firefighter Mike Chiapperini's funeral on Sunday.
While silent on motive, Spengler's suicide note did alert authorities to how he got the semiautomatic rifle and the 12-gauge shotgun he had with him Dec. 24. Spengler had served 17 years in prison in the bludgeoning death of his grandmother and should not have had access to firearms.
Officials said a neighbor allegedly purchased the guns for him. Authorities have charged Dawn Nguyen, 24, with lying on a form for stating she would own the weapons.