Snipers operating from rooftops in Dallas killed five police officers and wounded six more in a coordinated attack during one of several protests across the United States against the killing of two black men by police this week.
Police described Thursday night's ambush as carefully planned and executed and said they had taken three people into custody before a fourth died. Dallas-based media said the suspect died from a self-inflicted gunshot wound after a standoff that extended into Friday morning.
The fourth suspect exchanged gunfire with police during the standoff at a downtown garage and warned of placing bombs throughout the city. Police have not yet confirmed his death but said no explosives have been found.
The attack came in a week that two black men were fatally shot by police officers in Baton Rouge, Louisiana, and outside Minneapolis. The killings, both now the subject of official investigations, inflamed tensions about race and justice in the United States.
The shots rang out as a protest in Dallas was winding down, sending marchers screaming and running in panic through the city's streets.
It was the deadliest day for police in the United States since the Sept. 11, 2001, attacks on New York and Washington.
A total of 12 police officers and two civilians were shot during the attack, Dallas Mayor Mike Rawlings told CBS News. Three of the officers who were shot were women, he said.
Rawlings said the people in custody, including one woman, were "not being cooperative" with police investigators. He said the assailant who was dead was being fingerprinted and his identity checked with federal authorities.
Police were still not certain they knew all of the individuals involved in the attack, Rawlings said.
No motive has been given for the shootings at the downtown protest, one of many held in major cities across the United States on Thursday. New York police made more than a dozen arrests on Thursday night, while protesters briefly shut down one of Chicago's main arteries.
One of the dead officers was identified as Brent Thompson, 43. He was the first officer killed in the line of duty since Dallas Area Rapid Transit formed a police department in 1989, DART said on its website. Thompson joined DART in 2009.
Dallas Police Chief David Brown said the shooters, some in elevated positions, used rifles to fire at the officers in what appeared to be a coordinated attack.
"(They were) working together with rifles, triangulating at elevated positions in different points in the downtown area where the march ended up going," Brown told a news conference, adding a civilian was also wounded.
"It has been a devastating night. We are sad to report a fifth officer has died," Dallas police said on Twitter.
A video taken by a witness shows a man with a rifle crouching at ground level and shooting a person who appeared to be wearing a uniform at close range. That person then collapsed to the ground.
Reuters could not immediately confirm the authenticity of the video.
President Barack Obama, who was traveling in Poland, expressed his "deepest condolences" to Rawlings on behalf of the American people.
"I believe I speak for every single American when I say that we are horrified over these events and we are united with the people and police department in Dallas," he said.
Obama said the FBI was in contact with Dallas police and that the federal government would provide assistance.
"We still don't know all of the facts. What we do know is that there has been a vicious, calculated and despicable attack on law enforcement," he said.
The shooting, which erupted shortly before 9 p.m. CDT (0100 GMT), occurred near a busy area of downtown Dallas filled with restaurants, hotels and government buildings.
Mayor Rawlings advised people to stay away on Friday morning as police combed the area. Transportation was halted and federal authorities stopped commercial air traffic over the area as police helicopters hovered.
Large sections of downtown remained closed to the public on Friday morning.
The Dallas-Fort Worth metropolitan area is one of the nation's most populous and is home to more than 7 million people.
The Dallas shooting happened as otherwise largely peaceful protests unfolded around the United States after the shooting of Philando Castile, 32, by police near St. Paul, Minnesota, late Wednesday. His girlfriend posted live video on the internet of the bloody scene minutes afterward, which was widely viewed.
Over the last two years, there have been periodic and sometimes violent protests over the use of police force against African-Americans in cities from Ferguson, Missouri, to Baltimore and New York. Anger has intensified when the officers were acquitted in trials or not charged at all.
'THE END IS COMING'
The suspect in the Dallas standoff had told police "the end is coming" and that more police were going to be hurt and killed. Police chief Brown said the suspect also told police "there are bombs all over the place in this garage and downtown".
Police said they were questioning two occupants of a Mercedes they had pulled over after the vehicle sped off on a downtown street with a man who threw a camouflaged bag inside the back of the car. A woman was also taken into custody near the garage where the standoff was taking place.
"We are leaving every motive on the table on why this happened and how this happened," Brown said.
Mayor Rawlings visited the wounded at Parkland hospital, the same hospital where President John F. Kennedy was taken after he was shot in Dallas in November 1963.
"(The attack) does have a very strange feel to it," Texas Attorney General Ken Paxton told CNN. "There is something missing here. Obviously there is a lot of information we don't have."
Outside the hospital, officers stood in formation and saluted as bodies of the officers were about to be transported.
(Reporting by Brendan O'Brien in Milwaukee, Eric M. Johnson in Seattle, Jon Herskovitz in Austin, Texas, Letitia Stein in Tampa, Florida; Writing by Scott Malone and Jon Herskovitz; Editing by Alison Williams and Jeffrey Benkoe)
The shooting comes at a time of fierce national debate and heightened scrutiny over the use of excessive force by police, especially against black men, in major U.S. cities, such as New York, Baltimore and Chicago.
Posts on Twitter showed the demonstrators gathered outside the Triple S Food Mart convenience store in Baton Rouge, where, police said in a statement, the man, Alton Sterling, 37, was shot by officers soon after midnight.
"No justice, no peace," chanted the protesters, who held up signs and occasionally blocked traffic, in images transmitted by media outlets in Baton Rouge.
Police officials were not immediately available to comment on the shooting or the protest. Reuters could not immediately trace relatives of Sterling, or a representative, to seek comment.
At about 12:30 a.m. on Tuesday, two police officers responded to a disturbance at the convenience store where they encountered Sterling, the Baton Rouge Police Department said.
"Uniformed officers responded to a disturbance call from a complainant who stated that a black male who was selling music CDs and wearing a red shirt threatened him with a gun," it added.
Sterling was shot in the ensuing altercation and died at the scene. The officers where placed on administrative leave, police said.
Several news stations on Tuesday evening aired what they said was cell phone video of the incident. It showed an officer using a stun gun on a red-shirted black man in a store parking lot and ordering him to get on the ground.
The two officers then tackled the man to the ground, and one pulled a gun from his holster to point it at the man's chest, the video showed.
At least three gunshots then ring out on the video clip, followed by the sound of a woman screaming and crying and a man asking whether "they shot him."
(Reporting by Brendan O'Brien in Milwaukee; Editing by Clarence Fernandez)