Two volunteer firefighters were shot dead on Monday by a convicted killer who lay in wait after setting a house alight to lure them to the scene.
The gunman, identified by police as William Spengler, 62, also injured two other firefighters in the Christmas Eve ambush in Webster, a quiet town on the Lake Ontario shore, 15 miles from Rochester.
When the first responders arrived to tackle the blaze, Spengler opened fire like a sniper, police said. He was armed with several weapons, including a rifle.
Spengler had served nearly two decades behind bars for the manslaughter of his grandmother and could not have owned the weapons legally. He was later found dead, apparently from a self-inflicted gunshot wound.
His sister, Cheryl, remained unaccounted for, police said. It is feared she may too have been shot by her brother, or have died in the blaze which began in the house they shared. It is believed their mother, Arline, also resided at the property until her death in October.
The ambush took place at around 6am, shortly after the town's volunteer fire service had been made aware of a burning property and car on Lake Road.
Webster police chief Gerald Pickering told reporters that the fire was probably set by Spengler "who then laid in wait with armament". He had picked a nearby vantage point from where he could observe the firefighters' movements.
"He took up a position of cover, to be a sniper and shoot the first responders," Pickering said
"We know that there were several different types of weapons," he added.
Earlier on Monday, Pickering fought back tears as he revealed the names of the two men who were killed – including a police lieutenant who gave up his free time to volunteer at the local fire station.
Mike Chiapperini, 43, was a public information officer for Webster police department. Tomasz Kaczowka, whose age was not released, was a 911 dispatcher.
"These people get up in the middle of the night to go put out fires. They don't expect to be shot and killed" said Pickering.
"These guys are all heroes, they are heroes," he said later.
An off-duty police officer who happened to be driving past the scene was also injured by shrapnel.
The first police officers to arrive at the scene returned fire and spent some time chasing the gunman. Meanwhile 33 people were evacuated from the neighbouring properties.
Fire crews were forced to wait until the area had been secured, with the help of Swat teams, before tackling the fire which by then had spread to nearby buildings. In all, seven homes were destroyed, police said.
"We do not know if there are any additional victims in these homes," Pickering said.
The two surviving firefighters in the attack suffered "significant injuries", a hospital spokeswoman said. Joseph Hofsetter received a complex bullet wound to the pelvis, while Theodore Scardino was hit in his right knee and left shoulder.
Both remained in an intensive care unit at hospital in nearby Rochester on Monday. Neither man's injuries are life threatening, but they are likely to need lengthy medical treatment, a hospital spokeswoman said.
Details of Spengler's criminal record were released by police later on Monday.
In 1981, he was given an indeterminate jail sentence after being convicted of beating his 92-year-old grandmother to death. The manslaughter conviction saw him spend more than 17 years in prison before his release in 1988.
Authorities said he remained on parole until 2006, but that there were no further recorded incidents of brushes with the law.
Pickering said that Monday's attack highlighted the need for the US to get a handle on gun control and mental health issues.
Monroe County Sheriff Patrick O'Flynn also lamented the rise in incidents of mass shootings. "It's sad to see that this is becoming more commonplace in communities across the nation," he said.
The deaths come amid renewed demands for tougher gun laws, after the Newtown school shooting 10 days ago in which 20 children and seven adults were killed. On Sunday, the most powerful gun rights lobby group in the US, the National Rifle Association, vowed again to oppose any new restrictions and said it would not cooperate with a task force on gun violence which is to be led by vice-president Joe Biden.
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