DALLAS — Two snipers shot 10 police officers from a building during a protest against police brutality, killing three, Dallas Police Chief David O. Brown said in a statement Thursday night.
Brown said two officers were in surgery and three were in critical condition.
"An intensive search for suspects is currently underway," he said. "No suspects are in custody at this time."
Minutes earlier, Dallas Area Rapid Transit tweeted that four of its officers had been shot and one of them had died. The three others had non-life-threatening injuries.
One police officer was taken to Parkland Memorial Hospital, the same hospital where President John F. Kennedy was pronounced dead after being shot Nov. 22, 1963, WFAA reported. A hospital representative referred questions to Dallas Police.
Live video feeds from news organizations and reports from witnesses painted a picture of a chaotic scene, with police cars converging on a downtown building.
Marchers protesting police shootings were moving down Lamar Street near Griffin when shots were fired.
One witness told The Dallas Morning News that he heard "what sounded like six to eight shots."
A bystander who was at the scene told WFAA the shooter stood by as the rally passed him, then opened fire on officers.
Another bystander, Richard Adams, said the protest was "a lovely, peaceful march," until they were walking down Commerce Street near the Bank of America building parking garage when he heard what sounded like "a bunch of firecrackers going off."
"Everybody just stopped — 'Run, run for your lives!' Women with children and babies and everybody was chaotically running. And then, maybe I was a half-a-block away, calming down a little bit when we heard it again. [...] There must have been five times tonight — whenever we thought we were safe, people said 'Run, people were shot!'"
According to the Dallas police scanner, officers were looking for a light-skinned black male about 14 years old who was armed with AR-15 type assault rifle. He was described as wearing black shorts and a camouflage shirt.
Police were looking at videotape to get better idea of where the suspect might be, according to the scanner feed.
Before shots rang out, the Dallas Police Department was live-tweeting the protest, even posting photos of officers posing with demonstrators.
Meanwhile, peaceful marches and demonstrations took place in cities across the nation, including New York, Washington and Chicago, to protest shootings of black men by police.
Thousands of people gathered Thursday at the school where Philando Castile worked, mourning the man's death at the hands of police officers Wednesday.
Demonstrators gathered outside Minnesota Gov. Mark Dayton's residence, where a little after 4:30 p.m. CT the governor waded into the crowd to talk to protesters.
Then people marched to St. Paul's J.J. Hill Montessori school, where Castile was a cafeteria supervisor.
His mother, Valerie Castile, stood on a picnic table there to address the crowd.
Castile, 32, was shot Wednesday evening by a St. Anthony police officer during a traffic stop in Falcon Heights, allegedly for a broken taillight.
Castile was behind the wheel when an officer asked him to present his license and registration. According to a video posted to Facebook by Castile's girlfriend, Lavish Reynolds, the shooting occurred when Castile told the officer that he was going to reach for his wallet to get his ID but also told the officer he had a firearm on him, which he was licensed to carry.
The graphic Facebook Live post had been seen by more than 4.7 million viewers as of Thursday evening.
Castile's death came just one day after Baton Rouge, La., officers Blane Salamoni and Howie Lake II shot and killed Alton Sterling outside a convenience store. The officers responded to an anonymous call from someone claiming a man selling CDs outside a Triple S Food Mart threatened him with a gun. After police arrived, some type of struggle ensued and Sterling, 37, was fatally shot in the chest and back. The officers were placed on administrative leave pending an investigation.
About 500 people led by a friend of Sterling's protested outside of a church prayer vigil Thursday evening in Baton Rouge.
Chermicka Brown said more and more people have joined her efforts since she began protesting, on foot, in different regions of Baton Rouge Tuesday following the police shooting death of Sterling.
While waving signs and shaking tambourines and other noisemakers, the protestors chanted, "No justice, no peace, no racist police" as they marched through the Living Faith Christian Center parking lot Thursday evening.
Their chants echoed as they piled together in the church's breezeway, some shouting that attending a church vigil would not bring justice to Sterling.
Brown said she has mainly protested in the areas adjacent to where the shooting occurred.
She said she plans to lead protesters to other parts of Baton Rouge, such as downtown, in the coming days and that she will continue protesting, even cross country if necessary, until justice is served.
An estimated 3,500-4,000 people gathered at the Living Faith Christian Center, about one mile from the store where Sterling was fatally shot.
Gov. John Bel Edwards addressed the crowd before 12 area pastors spoke about keeping the faith, finding peace and seeking justice following Tuesday's event.
In New York, a massive sit-in disrupted traffic in the heart of Midtown Manhattan.
Later, police asked people to disperse.
And then began arresting demonstrators while others chanted, "let them go, let them go."
In Chicago, protests seemed to be led mostly by young people.
In Seattle, people gathered to hear organizers say, "We have to stop doing business as usual."
And outside the White House, people gathered to protest against police brutality.
Then marched to the U.S. Capitol.
House Democrats came out of the Capitol to join protesters on the steps. U.S. Rep. John Lewis, D-Georgia, a longtime civil rights activist, told the protesters: "What happened in Minnesota and Louisiana is a shame and a disgrace and must never, ever happen again."
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Contributing: Melanie Eversley and Michael Burke, USA TODAY, Megan Wyatt, The (Lafayette, La.) Daily Advertiser, and KARE-TV, Minneapolis-St. Paul 
