(CNN) -- William Spengler had killed before.
The first time, presumably, was in 1980. Then about 40 years old, Spengler struck his grandmother with a hammer. A year later, he was convicted of first-degree manslaughter in her death.
Flash forward to before dawn Monday, in Webster, New York, a town of about 43,000 people located 10 miles east of Rochester. 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.
When local firefighters arrived at the scene, Spengler fired and killed again.
Authorities haven't given a motive for the latest violence, which left two firefighters dead and two other firefighters and an off-duty police officer from a nearby town wounded.
And they can't ask the shooter, who was found dead of a self-inflicted gunshot wound to the head around 11 a.m., about six hours after first calls about the fire came in.
But the Webster police chief has his own idea about why this happened.
"Just looking at the history, obviously this is an individual who had a lot of problems, to kill his grandmother," Pickering said. "And I'm sure there were ... mental health issues involved."
After his 1981 manslaughter conviction, Spengler was given an indeterminate sentence, said Monroe County District Attorney Sandra Doorley.
He ended up spending nearly 18 years behind bars until his release in 1998. 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.
Nor, Pickering said, had police had any "contact with him criminally" in the recent past.
By then, Spengler was living in a home in Webster, likely with his sister, who was still unaccounted for Monday afternoon. Their mother had died sometime in the past year, according to Pickering.
He'd accumulated weapons, bringing "several different types" with him before the shootings, the police chief said. It is not known how he obtained these firearms, but ex-felons are not allowed to possess weapons.
But because Spengler had them, two families are in mourning. Many of his former neighbors are homeless, because having a gunman on the loose slowed fire crews' efforts to corral a blaze that eventually destroyed seven homes.
"It's Christmas Eve. This is a day where people are getting together to celebrate a holiday," Lt. Gov. Bob Duffy told reporters in Webster. "This tragedy is just unthinkable and unspeakable."