Two volunteer firefighters have been shot dead and two others injured when a gunman opened fire as they were responding to a house fire in New York state.
The gunman, named as William Spengler, opened fired on the four men as they arrived shortly after 5:30am on Monday to put out the blaze in Webster, said police chief Gerald Pickering.
Spengler set fire to a car and house to lure the firefighters to his house on the shore of Lake Ontario.
"It does appear it was a trap," an emotional Mr Pickering said at a news conference.
Spengler, 62, had served more than 17 years in prison for beating his 92-year-old grandmother to death with a hammer in 1980 at the house next to where the attack happened.
Police said Spengler died at the scene after shooting himself in the head.
One of the firefighters who died, Mike Chiapperini, was also a town police lieutenant, but it was not clear whether he returned fire.
The other firefighter who was killed was named as Tomasz Kaczowka.
The two wounded firefighters, named as Joseph Hofsetter and Theodore Scardino, remained in a critical condition in hospital.
Police were concerned that Spengler's sister, Cheryl Spengler, was in the house where the fire started, reports said.
Spengler reportedly lived there with his sister and mother, Arline Spengler, who died in October.
An off-duty police officer who was driving past the scene also has injuries from shrapnel, Mr Pickering said.
The fire spread and destroyed six other homes in the quiet lakeside town, around 340 miles (550 km) northwest of New York City.
The gunfire initially kept firefighters from battling the blaze.
The neighbourhood's residents were evacuated and searched by police, and a SWAT team was called to the scene.
New York Governor Andrew Cuomo said the shooting was a "senseless act of violence" and offered his condolences to the victims' families.
"New York's first responders are true heroes as they time and again selflessly rush toward danger in order to keep our families and communities safe," he said.
Monroe county sheriff Patrick O'Flynn said: "It's sad to see that that this is becoming more commonplace in communities across the nation."
The shooting in Webster comes 10 days after the shooting rampage at a school in Newtown , Connecticut, in which 20 children and six adults were killed.
The Newtown massacre has revived debate in the United States on the country's gun laws, which are far more lax than in most other developed nations.