Authorities used an armored vehicle to help residents flee dozens of homes on the shore of Lake Ontario a day before Christmas. Police restricted access to the neighborhood, and officials said it was unclear whether there were other bodies in the seven houses left to burn.
The gunman's sister, who lived with him, was unaccounted for. The gunman's motive was unknown.
William Spengler fired at the four firefighters when they arrived shortly after 5:30 a.m. at the blaze in Webster, a suburb of Rochester, town police Chief Gerald Pickering said. The first police officer who arrived chased the gunman and exchanged shots.
Spengler lay in wait outdoors for the firefighters' arrival, then opened fire probably with a rifle and from atop an earthen berm, Pickering said.
"It does appear it was a trap," he said.
Spengler had served more than 17 years in prison for beating his 92-year-old paternal grandmother to death with a hammer in 1980 at the house next to where Monday's attack happened, Pickering said. Spengler, 62, was paroled in 1998 and had led a quiet life since, authorities said. Convicted felons are not allowed to possess weapons.
Two firefighters, one of whom also was a town police lieutenant, died at the scene, and two others were hospitalized. An off-duty officer who was passing by also was injured.
Another police officer, the one who exchanged gunfire with Spengler, "in all likelihood saved many lives," Pickering said.
Emergency radio communications capture someone saying he "could see the muzzle flash coming at me" as Spengler carried out his ambush. The audio posted on the website RadioReference.com has someone reporting "firefighters are down" and saying "got to be rifle or shotgun — high powered ... semi or fully auto."
Spengler lived in the house with his sister, Cheryl Spengler, and his mother, Arline Spengler, who died in October. He had originally been charged with murder in connection with grandmother Rose Spengler's death but pleaded guilty to a reduced charge of manslaughter.
A friend said William Spengler didn't seem violent but hated his sister. Roger Vercruysse lived next door to Spengler and recalled a man who doted on his mother, whose obituary suggested contributions to the West Webster Fire Department.
"He loved his mama to death," said Vercruysse, who last saw his friend about six months ago. "I think after his mama passed, he went crazy."
Vercruysse also said Spengler "couldn't stand his sister" and "stayed on one side of the house and she stayed on the other."
The West Webster Fire District learned of the fire early Monday after a report of a car and house on fire on Lake Road, on a narrow peninsula where Irondequoit Bay meets Lake Ontario, Monroe County Sheriff Patrick O'Flynn said.
The fire appeared from a distance as a pulsating ball of flame glowing against the early morning sky, flames licking into treetops and reflecting on the water, with huge bursts of smoke billowing away in a brisk wind.