Three police officers have been killed by a gunman in Pittsburgh - the second mass shooting in the US in 24 hours.
The officers were responding to an emergency call from the house of the gunman, named as Richard Poplawski, 23.
Police said he was waiting, armed with rifles and a bulletproof vest. He shot two officers as they entered the house, and a third who tried to help them.
He then traded gunfire with police for four hours before being injured and giving himself up.
His friends said he had recently lost his job, and was worried that US President Barack Obama was about to ban guns.
The shooting comes a day after a gunman killed 13 people in New York state.
'Lying in wait'
In a televised press conference, Pittsburgh police chief Nathan Harper said it was a "very sad day" for the city.
WEEK OF SHOOTINGS
Sat 4 April: Gunman kills three policemen in Pittsburgh before being wounded and captured
Fri 3 April: Gunman kills 13 people at an immigration centre in Binghamton, New York state, then apparently shoots himself
Sun 29 March: Gunman kills seven elderly residents and a nurse at a nursing home in Carthage, North Carolina, then is shot and wounded himself
Sun 29 March: Man kills five relatives and himself in Santa Clara, California
"Our hearts and our prayers go out to the officers who paid the ultimate sacrifice," he said.
Mr Poplawski was armed with two rifles, a pistol and a lot of ammunition, the authorities said.
Mr Harper said the emergency call had been made by the gunman's mother, who had apparently stayed in the basement of the house during the whole incident.
He said the gunman had been "lying in wait", and the first two officers who reached the house were shot in the head as they entered.
'Stockpiled food and guns'
Witnesses described how the officers who arrived after the shooting could not reach their stricken colleagues.
One neighbour, Don Sand, told the Associated Press: "They couldn't get the scene secure enough to get to them. They were just lying there bleeding.
"By the time they secured the scene enough to get to them it was way too late."
Police chief Nathan Harper on the shootings
Edward Perkovic, who said he was close to Mr Poplawski, told the Pittsburgh Post-Gazette how his friend had called him on his mobile phone during the incident, saying he had been shot in the leg and the chest.
Mr Perkovic said Mr Poplawski told him: "Eddie, I'm going to die today. Tell your family and friends I love them. This is probably the end."
Then there was a burst of gunfire and the call ended, Mr Perkovic said.
Another man who said he was a friend of Mr Poplawski, Aaron Vire, told the newspaper: "He said he'll be ready if there's ever an invasion of the United States and that he had stockpiled foods and guns for that eventuality."
Mr Poplawski has been charged with three counts of homicide, aggravated assault and a weapons violation.
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