N.Y. Firefighter Shooting Update: Gunman left note saying he wanted to "do what I like doing best, killing people"

(CBS/AP) WEBSTER, N.Y. -- The man who police say lured firefighters to his home and then ambushed them with a semi-automatic rifle left a note saying he wanted to burn down his neighborhood and "do what I like doing best, killing people," police said Tuesday.

PICTURES: Cops: NY ex-con gunned down firefighters

William Spengler, 62, who served 17 years in prison for manslaughter in the 1980 hammer slaying of his grandmother, set his house afire before dawn on Dec. 24, before taking a revolver, a shotgun and a semiautomatic rifle to a sniper position outside, Police Chief Gerald Pickering said.

Authorities say Spengler sprayed bullets at the first responders, killing two firefighters and injuring two others who remained hospitalized Tuesday in stable condition, awake and alert and expected to survive. He then killed himself as seven houses burned on a sliver of land along Lake Ontario.

Police recovered a military-style .223-caliber semiautomatic Bushmaster rifle with flash suppression, the same make and caliber weapon used in the elementary school massacre in Newtown, Conn., that killed 26, including 20 young children, Pickering said.

The chief said it was believed the firefighters were hit with shots from the rifle given the distance but the investigation was incomplete.

"He was equipped to go to war, kill innocent people," the chief said.

The two- to three-page typewritten rambling note left by Spengler did not reveal what set off the killer or provide a motive for the shootings, Pickering said. He called the attack a "clear ambush on first responders."

He declined to reveal the note's full content or say where it was found. He read only one chilling line: "I still have to get ready to see how much of the neighborhood I can burn down, and do what I like doing best, killing people."

As Pickering described it and as emergency radio communications on the scene showed, the heavily armed Spengler took a position behind a small hill by the house as four firefighters arrived after 5:30 a.m. to extinguish the fire: two on a fire truck; two in their own vehicles.

They were immediately greeted by bullets from Spengler, who wore dark clothing. Volunteer firefighter and police Lt. Michael Chiapperini, 43, driving the truck, was killed by gunfire as the windshield before him was shattered. Also killed was Tomasz Kaczowka, 19, who worked as a 911 dispatcher.

Several firefighters went beneath the truck to shield themselves as an off-duty police officer who was passing by pulled his vehicle alongside the truck to try to shield them, authorities said.

The first police officer who arrived chased and exchanged shots with Spengler, recounting it later over his police radio.

"I could see the muzzle blasts comin' at me. ... I fired four shots at him. I thought he went down," the officer said.

At another point, he said: "I don't know if I hit him or not. He's by a tree. ... He was movin' eastbound on the berm when I was firing shots." Pickering portrayed him as a hero who saved many lives.

The audio posted on the website RadioReference.com also has someone reporting "firefighters are down" and saying "got to be rifle or shotgun - high-powered ... semi or fully auto."

Spengler had been charged with murder in his grandmother's death but pleaded guilty to a reduced charge of manslaughter, apparently to spare his family a trial. After he was freed from prison, Spengler - a felon who wasn't allowed to possess weapons - had lived a quiet life on Lake Road on a narrow peninsula where Irondequoit Bay meets Lake Ontario.

That ended when he left his burning home Monday morning, armed with his three weapons and a lot of ammunition.

"I'm not sure we'll ever know what was going through his mind," Pickering said.

Complete coverage of the Webster firefighter shooting on Crimesider