A man opened fire on police officers in Pittsburgh, US, during a domestic disturbance call today, killing three of them, a police official said.
Friends said he had been upset recently about losing his job and that he feared the Obama administration was poised to ban guns.
Three officers were killed, said a police official at the scene who spoke on condition of anonymity because he was not authorised to speak to the media.
Police spokeswoman Diane Richard would only say that at least five officers were wounded, but would not give any other details.
Police planned to release more details later today.
The man who fired at the officers was arrested after a several-hour stand-off. One witness reported hearing hundreds of shots.
The shootings occurred just two weeks after four police officers were fatally shot March 21 in Oakland, California, in the deadliest day for US law enforcement since the September 11, 2001, terrorist attacks.
Police did not immediately release the gunman’s identity, but his friends identified him as Richard Poplawski, 23. They described him as a young man who thought the Obama administration would ban guns.
One friend, Edward Perkovic, said Poplawski feared “the Obama gun ban that’s on the way” and “didn’t like our rights being infringed upon”.
Another long-time friend, Aaron Vire, said Poplawski feared that President Barack Obama was going to take away his rights, though he said he “wasn’t violently against Obama”.
Mr Perkovic, a 22-year-old who said he was Poplawski’s best friend, said he got a call at work from him in which he said, “Eddie, I am going to die today. ... Tell your family I love them and I love you.”
Mr Perkovic said: “I heard gunshots and he hung up. ... He sounded like he was in pain, like he got shot.”
Mr Vire, 23, said Poplawski once had an internet talk show but that it was not successful. Mr Vire said Poplawski had an AK-47 rifle and several powerful handguns, including a .357 Magnum.
Another friend, Joe DiMarco, said Poplawski had been laid off from his job at a glass factory earlier this year. Mr DiMarco said he did not know the name of the company, but knew his friend had been upset about losing his job.
The officers were called to the home in the Stanton Heights neighbourhood at about 7am, Ms Richard said.
Tom Moffitt, 51, a city firefighter who lives two blocks away, said he heard about the shooting on his scanner and came to the scene, where he heard “hundreds, just hundreds of shots. And not just once – several times”.
Rob Gift, 45, who lives a block away, said he heard rapid gunfire as he was letting his dog out.
He said the neighbourhood of well-kept single-family houses and manicured lawns is home to many police officers, firefighters, paramedics and other city workers.
“It’s just a very quiet neighbourhood,” Mr Gift said.
According to the National Law Enforcement Officers Memorial Fund, 133 law enforcement officers died in the line of duty in the US in 2008, a 27% decrease from the year before and the lowest annual total since 1960.