The shooting happened at the end of a protest against the recent police shootings of two black men, Alton Sterling in Louisiana, and Philando Castile in Minnesota.
Dallas police said two snipers opened fire from an elevated position in a building, targeting police officers "ambush-style" and striking some in the back. One suspect later claimed to have planted bombs all over the downtown area.
The protest had been peaceful before the shooting erupted, according to witnesses. After the multiple shots rang out from a position above the crowd, hundreds of people began running in the opposite direction, as officers took cover and returned fire.
Dallas police said two people were later taken into custody - one described as a "person of interest" who turned himself in after his picture was circulated.
The person of interest was later determined to not be a suspect and was released from custody.
The second person taken into custody was described as a suspect who had engaged in a shootout with police.
Dallas police said the suspects had also made threats about planting a bomb in the area and FBI and ATF agents were called in to help search for a possible explosive device.
It has been a devastating night. We are sad to report a fifth officer has died.— Dallas Police Depart (@DallasPD) July 8, 2016
The active shooter situation continued late into the evening even after those two individuals were detained.
Police said they had a suspect cornered on the upper floor of a 10-story parking garage in downtown Dallas near the campus of El Centro College and they were negotiating with the person.
Dallas police Chief David Brown said after midnight local time that the suspect was still holed up in the garage and exchanging gunfire with officers, several hours after the initial incident.
"The suspect that we are negotiating with that has exchanged gunfire with us in the last 45 minutes had told our negotiators that the end is coming and he's going to hurt and kill more of us - meaning law enforcement," Brown said at a 12:30 a.m. press conference. "And there are bombs all over this place in this garage and in downtown. So we are being very careful in our tactics."
He said officers also took a woman into custody who was in the same area of the garage where the suspect was, but he did not elaborate on her possible role in the shootings.
In addition, officers followed two suspects who were seen putting a camouflage bag into a Mercedes and fleeing the scene. The suspects were pulled over in the area and detained and officers were interviewing them.
Earlier, police released a picture of the "person of interest" who was photographed at the rally wearing camouflage and carrying a rifle during the protest. Texas has open-carry laws allowing individuals to carry firearms.
The man was later released from custody and determined to not be a suspect.
A man believed to be the brother of the person of interest gave media interviews saying his brother was not the shooter.
Cory Hughes said his brother Mark had been carrying the rifle at the event, but turned it over to a police officer after the shooting occurred so he wouldn't be seen as a suspect, and he then went home.
Cory Hughes tweeted to a Dallas news anchor: "My brother and I are at the Dallas Police Station now! Please let the world Know he had nothing to do with this."
Video posted by the Dallas Morning News also appeared to show the same man in the camouflage shirt walking around calmly on the streets in the crowd after the shooting had occurred.
Additional video posted on social media showed the man handing over his rifle to a police officer voluntarily and exchanging information.
Facebook video of DPD's original person of interest, handing over his weapon to authorities— Mike Leslie (@MikeLeslieWFAA) July 8, 2016
Via facebook live videohttps://t.co/hDmeV6T4sz
Brown said that 11 officers had been shot by two snipers firing from an elevated position "ambush-style."
Five were killed, two were in critical condition and two were in surgery.
According to statistics from the National Law Enforcement Officers Memorial Fund, this was the deadliest attack on law enforcement since Sept. 11.
"We believe that these suspects were positioning themselves in a way to triangulate on these officers, do two different perches in garages in the downtown area," Brown said. "And they planned to injure and kill as many law enforcement officers as they could."
One civilian was also wounded.
BREAKING: DPD Chief David Brown says 10 officers were shot by 2 snipers in downtown Dallas. 3 are dead, 3 are critical, and 2 are in surgery— WFAA-TV (@wfaachannel8) July 8, 2016
The Dallas transit agency DART confirmed on Twitter that four of its officers had been shot and one was killed. The DART numbers were included in Brown's tally.
DART later identified the fallen officer as Officer Brent Thompson, 43, the first DART officer killed in the line of duty. He joined the agency in 2009.
Witnesses and police said it appeared the shooters used rifles that fired many shots in rapid succession.
"At 8:58 our worst nightmare happened," said Dallas Mayor Mike Rawlings. "Our Dallas public safety, Dallas Police Department, DART officers were fired upon by shooters. I'm sad to say that we have deceased. And it is a heartbreaking moment for the city of Dallas."
Four DART police officers were shot in downtown Dallas. 1 deceased, others not life-threatening. No IDs yet. Updates via twitter.— dartmedia (@dartmedia) July 8, 2016
Video from the scene showed a heavy police presence and officers taking cover behind vehicles on the street after the shooting.
Josh Stephen, a photojournalist who was covering the protest when the gunfire erupted, said the event had ended and people were calmly walking back when all of a sudden shots rang out and people started running in the opposite direction.
"As they all began to run east, you could hear gunfire, gunfire, gunfire, just rapid succession," he told ABC affiliate WFAA.
He also saw officers head into the possible line of fire to help a wounded colleague.
"I saw Dallas police officers bravely go in with a police car, pick him up, put him in the back seat of a car, and rush him to a hospital. They rushed him out of here so fast."
Reactions and expressions of sympathy to the shooting victims and their families poured in from Los Angeles and around the country.
Mayor Eric Garcetti tweeted: "Tonight's assassinations undermine our democracy and were an attack on us all. We cannot let hate spread like a disease in our country."
#LAPD is monitoring the tragedy in Dallas, there have been no incidents in LA and we will remain on heightened alert— LAPD Online News (@LAPDonlinenews) July 8, 2016
The Los Angeles Police Department said it was not on tactical alert after the Dallas shootings. "While we continue to monitor the evolving situation in Dallas, we offer our heartfelt condolences as a department to the families of the officers killed in tonight's attack in Downtown Dallas," the LAPD tweeted, using #WeStandWithDallas.
Our country depends on both those who protect our democracy and those who embody it. LA is with you Dallas.— Eric Garcetti (@ericgarcetti) July 8, 2016