Dallas shooting: who are the killers and everything else we know so far
Five police officers have been killed and another six injured after snipers opened fire on them from rooftops in Dallas at a protest on Thursday evening.
One sniper has been killed while exchanging gunfire with authorities in a parking garage downtown, said Dallas Police Chief David Brown, while three others are in custody.
Police officers surrounded a car park near El Centro College where an armed man was firing off rounds with a rifle.
The gunfire broke out around 8.45pm while hundreds of people gathered to protest after police shot dead two black men in Baton Rouge, Louisiana, and suburban St. Paul, Minnesota.
Mayor Mike Rawlings said one member of the public was also wounded in the gunfire.
The attack was one of the worst mass shootings of police in the USA's history.
Who are the killers?
The identities of the suspects are not yet known but police said the ambush appeared carefully planned and executed. Police chief Brown said the snipers fired "ambush style" upon the officers.
Three snipers have been arrested and a fourth, who told police negotiators he intended to hurt more law enforcement officials, has been killed. Local media have suggested he was killed after a self-inflicted gunshot but this has not yet been confirmed.
The suspect told police "the end is coming" and that more police were going to be hurt and killed. Brown said the suspect also told police "there are bombs all over the place in this garage and downtown".
One woman was taken into custody in the parking garage where the standoff occurred. Two others were taken into custody during a traffic stop.
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.
"We are leaving every motive on the table on why this happened and how this happened," Brown said.
The search for the shooters stretched throughout downtown, an area of hotels, restaurants, businesses and some residential apartments. The area is only a few blocks away from Dealey Plaza, where President John F. Kennedy was assassinated in 1963. Some of the injured officers were taken to Parkland Hospital.
The scene was chaotic, with helicopters hovering overhead and officers with automatic rifles on the street corners
The police have said they are still unsure of the attackers' motivation. Police chief Brown told how the attackers "triangulated" in the downtown area where the protesters were marching and had "some knowledge of the route" they would take.
Witnesses told journalists that the shooters appear to be organised and strategic.
Authorities have not determined whether any protesters were involved with or were complicit in the attack and were not certain early Friday that all suspects have been located, Brown said.
Who were the victims?
Four of the officers who were killed were with the Dallas Police Department. One was a Dallas Area Rapid Transit officer. The agency said in a statement that 43-year-old officer Brent Thompson was the first officer killed in the line of duty since the agency formed a police department in 1989.
"Our hearts are broken," the statement said.
Thompson is the only officer to have been identified so far.
Theresa Williams told AP that the injured civilian was her sister, 37-year-old Shetamia Taylor.
Williams said her sister was at the protests Thursday night with her four sons, ages 12 to 17.
When the shooting began, Taylor threw herself over her sons, Williams said. She was undergoing surgery early Friday after being shot in the right calf.
Is Dallas safe?
Mayor Rawlings has said that authorities will likely ask some people to stay away from downtown Dallas on Friday.
"This is still an active crime scene. We're determining how big that crime scene is," the mayor said.
A map will be posted online showing an area where people should avoid on Friday.
New York police made more than a dozen arrests on Thursday night, while protesters briefly shut down one of Chicago's main arteries.
Why were people protesting?
The use of force by police against African-Americans in cities from Ferguson, Missouri, to Baltimore and New York has sparked periodic and sometimes violent protests in the past two years and has spawned the Black Lives Matter movement.
Anger has intensified when the officers involved in such incidents have been acquitted in trials or not charged at all.
The 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 on Wednesday. His girlfriend posted live video on the internet of the bloody scene minutes afterward, which was widely viewed.
No specific 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.