Armed with a Smith and Wesson .38 revolver, a pump-action Mossberg shotgun, and, most chillingly, a .223 Bushmaster rifle rigged with a flash suppressor to conceal the source of fire, William Spengler, 62, crouched on an embankment behind a tree Monday while his car, home and the remains of his 67-year-old sister Cheryl were in flames.

When firefighters in Webster, N.Y., nine miles east of Rochester, exited their emergency vehicles to begin dousing the flames, Spengler opened fire, murdering two volunteer responders and wounding three others before taking his own life.

Local authorities announced Tuesday afternoon that they found a note by Spengler that exposed the mind of a psychopathic killer that proves what police suspected from the start: That Spengler lit his house on fire to attract his targets and then unleashed his fury at them.  

“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,” Police Chief Gerald Pickering said, reading from the two to three pages of typewritten notes at a press conference.

“Equipped to go to war” is how a police officer described the killer, according to the local ABC affiliate. The rifle Spengler employed was the same model used by Adam Lanza, 20, to slaughter 20 children and six adults at Sandy Hook Elementary School in Newtown, Conn., on Dec. 14.

After firefighters finally doused the flames that spread to seven residences, the question of the whereabouts of the attacker’s sister was likely answered by the remains investigators found in the torched Spengler home. Medical examiners had yet by Tuesday afternoon to confirm the identity of the remains.

Spengler, a felon who served 17 years for beating his grandmother to death with a hammer in 1980, was not legally allowed to own firearms under the state of New York’s relatively strict gun laws. Some states make it easier for felons to have their right to keep and bear arms reinstated; New York is not one of them. Theoretically Spengler could have bought his weapons at a gun show with impunity to his gun-possession ban, or he could have had someone else buy the weapons for him. Or he could have stolen them from a careless assault weapon owner.

The New York Times reported Tuesday that there had been recent gun thefts in the vicinity, but the federal Bureau of Alcohol, Tobacco, Firearms and Explosives has yet to determine the source of the weapons used in Monday’s cold-blooded assault on local heroes.