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A fifth police officer in Dallas has died after being ambushed Thursday night by two snipers who opened fire during a protest march over the officer-involved shootings of black men in Louisiana and Minnesota, authorities said.

“Our worst nightmare happened,” Mayor Mike Rawlings said at an evening news conference.

An estimated 800 people had gathered for a rally and protest march about two blocks from Dealey Plaza when the first shots rang out. One hundred police officers were providing security for the event, Dallas Police Chief David Brown said.

Two snipers started shooting at the officers “ambush style” from elevated positions just as the protest march was ending, according to Brown, who added that some of the officers had been shot in the back.

Four of the slain officers were members of the Dallas Police Department, one was an officer with the Dallas Area Rapid Transit agency.

Video from the scene showed hundreds of people running in all directions after the shooting started.

“In the midst of it, gunshots just started barreling out,” witness Michael Jackson told CNN’s Don Lemon. “I immediately started running the opposite way.”

G.J. McCarthy said at first he thought it was fireworks. Then it got louder, and protesters realized it was gunfire.

“That went on for a while,” he said. Crowds ran into the El Centro College parking garage, then spilled out after word spread that there was a sniper nearby.

Clarissa Myles said she was eating at a McDonald’s nearby when peaceful protests suddenly turned chaotic.

“Everyone was screaming, people were running,” she said. “I saw at least probably 30 shots go off.”

A witness who was at the protest, told KTVT he heard multiple gunshots.

“Whoever was shooting had an assault rifle — and I know guns. The shots were in rapid succession,” the witness said.

Witness Ismael Dejesus said he filmed the shooter from his hotel balcony about 50 yards away. He described the gunman as wearing tactical pants and a tactical shirt. He had a weapon with a “pretty big magazine,” he said.

“He got out of there, walked over to the pillar, put a magazine in and started firing,” he said. “It did look planned. He knew where to stand, he had ammo ready.”

Numerous officers could be seen crouching behind patrol cars. Others approached the area holding protective shields.

Two of the wounded officers were in surgery and two others were listed in critical condition, Brown said.

A person of interest whose photo was released by police turned himself in late Thursday.

A second suspect remained barricaded in the parking garage exchanging gunfire with police, Brown said. A suspicious package was discovered near the suspect’s location. The bomb squad was investigating.

According to Brown, the barricaded man told negotiators, “the end is coming” and claims there are bombs planted all around the city.

At least three other individuals have been taken in for questioning in connection with the ambush.

A woman was taken into custody near the parking garage.

Two other people were being questioned after an officer saw an individual carrying a camouflaged bag speed away from the area in a black Mercedes, a release from the City of Dallas stated. Officers followed the vehicle and took both occupants into custody.

Check back for updates on this developing story.