PITTSBURGH – A gunman wearing a bulletproof vest and "lying in wait" opened fire on officers responding to a domestic disturbance call Saturday, killing three of them and turning a quiet Pittsburgh street into a battlefield, police said.

Police Chief Nate Harper said the motive for the shooting isn't clear, but friends said the gunman recently had been upset about losing his job and feared the Obama administration was poised to ban guns.

Richard Poplawski, 23, met officers at the doorway and shot two of them in the head immediately, Harper said. An officer who tried to help the two also was killed.

Poplawski, armed with an assault rifle and two other guns, then held police at bay for four hours as the fallen officers were left bleeding nearby, their colleagues unable to reach them, according to police and witnesses. More than 100 rounds were fired by the SWAT teams and Poplawski, Harper said.

The three slain officers were Eric Kelly, 41, Stephen Mayhle, 29, and Paul Sciullo III, 37. Kelly had been on the force for 14 years, Mayhle and Sciullo for two years each. Another officer, Timothy McManaway, was shot in the hand and a fifth broke his leg on a fence.

Poplawski had gunshot wounds in his legs but was otherwise unharmed because he was wearing a bulletproof vest, Harper said. He was charged with three counts of homicide, aggravated assault and a weapons violation.

At 7 a.m., Sciullo and Mayhle responded to a 911 call from Poplawski's mother, who remained holed up in the basement during the entire dispute and escaped unharmed, Harper said. When they arrived at the home, Sciullo was immediately shot in the head. Mayhle, who was right behind him, was also shot in the head. "It appears he was lying in wait for the officers," Harper said.

Kelly, who was on his way home after completing his overnight shift when he heard the call for help, rushed to the scene and was killed trying to help Sciullo and Mayhle, Harper said. SWAT teams and other officers arrived and were immediately fired on as well. Don Sand, who lives across the street from Poplawski, said he was woken up by the sound of gunfire. Hunkering down behind a wall in his home, he saw the first two officers go down and then saw Kelly get shot.

"They couldn't get the scene secure enough to get to them. They were just lying there bleeding," Sand said. "By the time they secured the scene enough to get to them it was way too late."

Deputy Chief Paul Donaldson, who lives nearby, was one of the first officers to arrive. He saw Mayhle by a bush to the right of the door; Kelly was in the street and McManaway, his hand injured, was kneeling beside him, yelling that Kelly needed help. Donaldson suggested using a police van to get them. They draped a bulletproof vest on the window to protect the driver and several officers got into the van to get Kelly and McManaway. During this time, Poplawski was somehow distracted, Donaldson said. "We were fortunate that he didn't fire on us. I don't know why he was distracted, but he apparently didn't see us coming down to get them," he said. "It could have been worse."

Poplawski had feared "the Obama gun ban that's on the way" and "didn't like our rights being infringed upon," said Edward Perkovic, his best friend.

Perkovic, 22, 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." Perkovic said: "I heard gunshots and he hung up. ... He sounded like he was in pain, like he got shot."

Poplawski had once tried to join the Marines, but was kicked out of boot camp after throwing a food tray at a drill sergeant, Perkovic said.

Another longtime 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."

Vire, 23, said Poplawski once had an Internet talk show but that it wasn't successful. He said Poplawski owned an AK-47 rifle and several powerful handguns, including a .357 Magnum.

Obama has said he respects Americans' constitutional right to bear arms, but that he favors "common sense" gun laws. Gun rights advocates interpret that as meaning he would approve some curbs on assault and concealed weapons.

Poplawski had been laid off from his job at a glass factory earlier this year, said another friend, Joe DiMarco. DiMarco said he didn't know the name of the company, but knew his friend had been upset about it.

Poplawski had often fought with neighbors and had even gotten into fist fights with a couple, Sand said. "This is a relatively really quiet neighborhood except for him," Sand said. "He was just one of those kids that we knew to stay clear from."

Harper confirmed police had responded to calls from the Poplawski house several times but said the incidents were still being investigated.

Rob Gift, 45, who lives a block away, said the well-kept single-family houses with manicured lawns are home to many police officers, firefighters, paramedics and other city workers.

"It's just a very quiet neighborhood," Gift said.