Spengler was firing from "a natural depression" against a bank and a tree, he said.
William Spengler, 62, shot and killed two firefighters and apparently killed his sister in New York.
Spengler did not share the same closeness with his sister, with whom he shared his home, Vercruysse said.
After his 1981 manslaughter conviction, Spengler was given an indeterminate sentence, said Monroe County District Attorney Sandra Doorley.
Spengler of Vanderbilt Medical Center in Nashville calls for changes to the way medical journals handle conflicts of interest.
FORBES: Medical Journal Slams Medtronic Over Payments To Doctors
Monday to a 911 call, reporting a fire that Spengler is believed to have set, when the gunfire began, Pickering said.
Spengler was convicted in 1981 of first-degree manslaughter in the death of his grandmother and had been released on supervised parole.
By then, Spengler was living in a home in Webster, likely with his sister, who was still unaccounted for Monday afternoon.
Mr Vercruysse said that Mr Spengler "loved his mama to death", adding that he "went crazy" after she died in October.
BBC: US firefighters shot dead in 'ambush' in New York state
As a convicted felon, Spengler was not allowed to legally possess weapons.
Then about 40 years old, Spengler struck his grandmother with a hammer.
Spengler was convicted in 1981 of first-degree manslaughter in the death of his grandmother and had been released on supervised parole, Pickering said.
As a convicted felon, Spengler could not legally possess guns, but he had "several different types of weapons, " Webster Police Chief Gerald Pickering said.
Through 2006, Spengler was on supervised parole, during which time Doorley said she wasn't aware of any events suggesting he had gotten into further trouble.
That's when and where, Police Chief Gerald Pickering said, Spengler presumably set his and his sister's home ablaze, lugged weapons up a hill, then waited.
The note indicated Spengler's intentions, but not his motive, Pickering said.
Contacted by CNN by e-mail, Spengler's cousin, Shirley Ashwood, responded in an e-mail that her family had distanced itself from him after he killed his grandmother.
Spengler was especially attentive to his mother, who passed away in October, Vercruysse said, visiting her every day in the nursing home where she lived until she died.
Roger Vercruysse, described as a friend of William Spengler, was quoted by the Associated Press as saying that the shooter "couldn't stand" his sister, who lived with him.
BBC: US firefighters shot dead in 'ambush' in New York state
Spengler attributes this poke in the eye to a cold calculation by the Pacific rim types that the United States is no longer the region's dominant economic power.
Seven houses were destroyed and several others damaged by the fire, which investigators believe spread from a car parked next to the home where Spengler lived, Pickering said.
But because Spengler had them, two families are in mourning.
Spengler was especially attentive to his mother, who passed away in October, a former neighbor, Roger Vercruysse said, visiting her every day in a nursing home until she died.
Seven houses were destroyed and several others damaged by the fire, which investigators believe spread from a car parked next to the home where they believe Spengler lived, Pickering said.
Authorities do not know how William Spengler, 62, who was found dead hours after the four firefighters were shot, obtained the weapon or weapons he used or why he opened fire.
"The system failed all of us again, " she said, adding that her family grieved for the fallen firefighters -- one of whom her two daughters knew from school -- and Cheryl Spengler.
It will be a challenge for the medical examiner to determine if William Spengler's sister -- 67-year-old Cheryl Spengler -- was killed before the fire was set, because it was a "raging inferno, " Pickering said.
"Despite corporate profits being at a high, marketers are still taking a cautious approach in anticipation of lackluster consumer spending and, therefore, their willingness to invest in advertising is taking a conservative approach, " said Tim Spengler, chief executive officer of Magna Global.
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