The ex-convict who lured two firefighters to their deaths in a blaze of gunfire left a note saying he wanted to burn down the neighbourhood and "do what I like doing best, killing people," police in New York state said Tuesday as they recovered burned human remains thought to be the gunman's missing sister.

Police Chief Gerald Pickering said 62-year-old William Spengler, who served 17 years in prison for the 1980 hammer killing of his grandmother, armed himself with a revolver, a shotgun and a military-style rifle before he set his house on fire to lure first responders into a death trap before dawn on Christmas Eve.

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

Spengler had a .223-calibre semiautomatic Bushmaster rifle, the same make and calibre weapon used in this month's school shooting in Newtown, Connecticut, Pickering said.

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Lt. Michael Chiapperini, of both the Webster police and volunteer fire departments, has been identified as one of the firefighters killed Monday. (Webster Police Department)

Pickering declined to divulge the full content of Spengler's two- to three-page note, but he read one line from it: "I still have to get ready to see how much of the neighbourhood I can burn down, and do what I like doing best, killing people."

The human remains were found in the charred house that Spengler shared with his 67-year-old sister, Cheryl. A medical examiner will need to determine the identity and cause of death because the body is badly burned.

A friend said Spengler hated his sister, but the police chief said the note did not give a motive.

Spengler killed himself as seven houses burned around him Monday on a narrow spit of land along Lake Ontario.

Two firefighters were shot dead in the ambush, and two others were hospitalized in stable condition.

Authorities said Spengler hadn't done anything to bring himself to their attention since his parole. As a convicted felon, he wasn't allowed to possess weapons. Monroe County District Attorney Sandra Doorley said Spengler led a quiet life after he got out of prison.

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William Spengler served 17 years in prison after the beating death of his 92-year-old grandmother in 1980, after pleading guilty to a reduced charge of manslaughter. (Monroe County Sheriff's Office/Associated Press)

A friend, Roger Vercruysse, lived next door to Spengler and recalled a man who doted on his mother.

"He loved his mama to death," said Vercruysse, who last saw his friend about six months ago.

Vercruysse also said Spengler "couldn't stand his sister" and "stayed on one side of the house and she stayed on the other."

The dead men were identified as police Lt. Michael Chiapperini, 43, the Webster Police Department's public information officer; and 19-year-old Tomasz Kaczowka, also an emergency dispatcher.

Pickering described Chiapperini as a "lifetime firefighter" with nearly 20 years in the department, and he called Kaczowka a "tremendous young man."