Just after 3am local time, Dallas police updated the death toll.

The first shooters appear to have been positioned above the crowd when they opened fire around 8:45pm local time, the AP reported. Multiple rounds of shots could be heard on one video shot and posted on Facebook, apparently by a protest attendee.

Brown initially said that snipers shot at 10 officers. Local reports put the number at 11.

The shooting occurred just blocks from The Sixth Floor Museum at Dealey Plaza, on the site where Lee Harvey Oswald shot US president John F. Kennedy in 1963. The hurt officers were taken to two nearby hospitals.

The Dallas police department circulated a photo of a possible suspect who was marching in the protest, but his involvement was quickly questioned on social media.

That person of interest turned himself in, Brown said. He was later released from custody, according to local news reports.

Police also had in custody a female who was in the area of the garage where a suspected shooter was negotiating with police, along with two suspects with camouflage bags who were stopped in their Mercedes in the nearby neighborhood of Oak Cliff after a chase.

Brown said police are assuming that the person shooting at them in the garage, along with the people who were apprehended, were working together.

“We still don’t have a complete comfort level that we have all the suspects,” Brown said, promising a “very, very rigorous investigation and search of downtown [Dallas].”

The suspects were being interrogated to determine their motivation, including whether they were complicit with the organizers of march, he added.

Next Generation Action Network, the local group that organized the rally, posted a statement on Facebook saying its intentions were peaceful and that it did not condone violence.

The dead included members of the Dallas Police Department and at least one Dallas Area Rapid Transit police officer.

Dallas mayor Mike Rawlings said he has “heard from both the White House and the governor’s office extending their help.”

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