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.

The shooting occurred just two weeks after four police officers were fatally shot in Oakland, Calif., in the deadliest day for U.S. law enforcement since Sept. 11, 2001. The officers were the first Pittsburgh city officers to die in the line of duty in 18 years.

“This is a solemn day and it’s a very sad day in the city of Pittsburgh,” Harper said. “We’ve seen this kind of violence happen in California. We never would think this kind of violence would happen in the city of Pittsburgh.”

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.