The shootings occurred when police responded to a 911 call that a man dressed in black and armed with what appeared to be an assault-style rifle was walking near a shopping plaza about a mile from police headquarters. The deaths shocked a nation already on edge over recent killings by police, a run of violence that began July 5 in Baton Rouge and which has now left 10 dead, including eight law enforcement officers and two residents killed by police.

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Two city policemen and one sheriff’s deputy were fatally wounded, and another sheriff’s deputy was critically injured, said Col. Michael Edmonson, the superintendent of the Louisiana State Police at an afternoon news conference.

The alleged gunman, who was shot and killed during the exchange of gunfire, was later identified as Gavin Long, an African-American resident of Kansas City, Missouri, who turned 29 on Sunday,and was in Baton Rouge celebrating his birthday, according to relatives. In the spring of 2012, Long was named to the dean’s list at the University of Alabama, which he attended for one semester, university officials said.

With the circumstances of the shootings unexplained Sunday night, a community already numbed found itself searching for new words to describe its horror and despair.

“Stop this killing. Stop this killing. Stop this killing,” said Veda Washington-Abusaleh, the aunt of Alton Sterling, the 37-year-old man killed by Baton Rouge police on July 5.

“That’s how this all started, with bloodshed. We don’t want no more bloodshed.  … Because at the end of the day, when these people call these families and they tell them that their daddies and their mommies not coming home no more, I know how they feel, because I got the same phone call,” she said, breaking down in tears during an interview Sunday by a Baton Rouge TV station.

Within minutes of the 911 call, a barrage of gunfire was heard from the vicinity of Airline and Old Hammond highways in east Baton Rouge, a commercial area dotted with convenience stores, gas stations and discount clothing shops.

Louisiana is an open-carry state where no permits are required to buy or carry firearms.

Baton Rouge has been besieged in recent years by racial tension between its predominantly black residents and predominantly white police officers. Over the past two weeks, protesters marched almost daily over the same streets that police quickly barricaded Sunday morning.

One of the dead officers was Montrell Jackson, 32, an African-American, married and with a baby. Although his name had not yet been released by authorities Sunday evening, multiple sources, including relatives, confirmed he was among those killed.

The father of Matthew Gerald, a white officer, also confirmed Sunday that his 41-year-old married son, the father of two daughters, was another police officer killed.

Before joining the Baton Rouge Police Department last year, Gerald served in both the Marines and the Army, according to Ryan Cabral, a friend who served with him in Iraq.

“Matt was the kind of guy that you knew immediately when he entered the room,” Cabral said. “Whether it was the energy he carried with him or that Cajun accent he had … maybe it was the Marine in him.”

The third fatality was identified by the local newspaper, the Advocate, as Brad Garafola, 45, who served with the East Baton Rouge Parish Sheriff’s Office. He was working extra duty at the B-Quik convenience store on Airline Highway early Sunday morning, according to his wife, Tonja, and was headed home to begin vacation when he was gunned down.

“Everybody on this street depended on him,” Tonja Garafola said.

A cousin of Long’s, who spoke to The Washington Post on the condition of anonymity because he feared for his job, said Long was quiet, smart and had recently written a book about his travels around the world. The man said that Long, as far as he knew, had not expressed any particular outrage over the shootings of young black men by police.”I can’t see my cousin doing nothing like that,” he said. “Right now, I’m at a loss for words.”

Long served five years in the Marine Corps as a data network specialist, from August 2005 to August 2010. He left active duty as a sergeant. Records released by the Marine Corps on Sunday showed that he deployed once to Iraq from June 2008 to January 2009. He did not experience direct ground combat. He was assigned to units in Miramar, Calif., and Okinawa, Japan, during his military career.

In the hours after the shooting, police warned people living in the area of the gun battle to stay inside as they sought two other potential suspects. By the afternoon, dozens of law enforcement and emergency vehicles were on the scene, and police helicopters hovered overhead. Agents for the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives were also called to the scene, according to Attorney General Loretta Lynch, who said in a statement, “there is no place in the United States for such appalling violence.” President Obama as well as other government and law enforcement officials strongly condemned the shooting.

“It’s just very senseless and tragic,” said Chris Nassif, president of the Louisiana Union of Police, a statewide association of municipal police departments. “You’re seeing law enforcement targeted for doing their jobs.”

Nassif and colleagues from around the state had traveled to Baton Rouge during the protests that roiled the city last week.

“They seemed to have everything under control, and then this happens,” he said. “It just takes the breath out of you.”

Sunday’s gun battle occurred in a subdivision of Baton Rouge known as Tara, about five miles from where Sterling was killed. Protesters have gathered there nightly.

Sterling’s death was followed just 24 hours later, on July 6, by that of Philando Castile, a 32-year-old African-American who was shot during a traffic stop in St. Paul, Minn.

Then, on July 7, during a peaceful protest of those deaths, four policemen and a transit officer were killed by a lone gunman in Dallas.

Across the country, police have been on heightened alert, with many towns and cities mandating that officers not work their beats alone, and residents in places such as East Baton Rouge afraid to spend time outside their homes.

In Sunday’s incident, it was a sunny, breezy morning in Baton Rouge when shots were heard around 8:40 a.m. Police reported “officers down” at 8:44, according to Edmonson, the Louisiana State Police superintendent. Minutes later, the alleged gunman was also dead.

One Tara neighborhood woman, who asked that her name not be used, was playing tennis with her husband and two children when she first heard the gunfire.

“We have been in the house so much because of all of this going on, so we wanted to be outside,” she said. “I feel trapped in our own home. … I thought we would be safe here because we are close to a police station.”

The three deaths Sunday brought the total number of officers killed in the line of duty to 30 so far this year – up from about 16 at this point last year. The average mid-year total, according to FBI data, is about 25.

At an annual gathering of the National Organization of Black Law Enforcement Executives in Washington, an educational conference attended by police chiefs around the country, the mood was heavy with the Baton Rouge news. This weekend was the organization’s 40th anniversary celebration.

“It felt like a punch in the gut,” said Vera Bumpers, chief of police for the Houston Metro Police Department. “It resonated with everybody. The room was just like a hush and a rasp, like ‘not again.’ ”

It was a sentiment shared by Wanda Dunham, the chief of police for the Metropolitan Atlanta Rapid Transit Authority.

“Here we go again,” she recalled thinking. “Some people are still thinking about what happened in Dallas.

“I don’t want this to be the new normal,” she said. “So we have to start talking to the community before these things happen.”

President Obama asked the nation to refrain from “overheated” political discourse on the eve of the Republican and Democratic conventions.

“Regardless of race, political party or profession … everyone right now, focus on words and actions that can unite this country rather than divide it further,” he said. “We need to temper our words and open our hearts – all of us.”

Black activists also expressed outrage at the Baton Rouge police deaths.

“We’re all grieving. We’re still grieving the loss of Alton Sterling. We don’t value any life more than any other life,” said Ada Goodly, an attorney and activist with the National Lawyers Guild in Baton Rouge, who had been involved in the recent protests.

Jocelyn Jackson said she understands the anger behind the Black Lives Matter movement but added that “God gives nobody the right to kill and take another person’s life. … It’s coming to the point where no lives matter,” she said, “whether you’re black or white or Hispanic or whatever.”