(CNN) — The ambush began with gunshots that killed five officers and sent screaming crowds scrambling for cover. It ended when a Dallas police bomb squad robot killed a gunman after negotiations failed.
Investigators have identified the dead suspect: 25-year-old Micah Xavier Johnson of Mesquite, Texas. But they're still trying to answer key questions. Chief among them: Was anyone else involved in the shootings, which began Thursday night during a protest against police violence and left parts of downtown Dallas under siege for hours? And are other suspects on the loose?
The deadly gunfire erupted in Dallas as videos showing two African-American men shot by police in Louisiana and Minnesota spurred protests and debate over police use of force across the country.
Five police officers were killed and seven others were injured in the ambush. It was the deadliest single incident for U.S. law enforcement since September 11, 2001. Two civilians also were injured in the shootings, the Dallas mayor's office said.
As officials condemned the attack Friday, details emerged about the suspect who died after a lengthy standoff with police in a parking garage.
The suspect told police negotiators that he was upset about recent police shootings, that he wanted to kill white people -- especially white officers -- and that he acted alone, the city's police chief told reporters Friday.
Dallas sniper attack: 5 officers killed, suspect identified
By Faith Karimi, Catherine E. Shoichet and Ralph Ellis, CNN
Updated 1:58 PM ET, Fri July 8, 2016
Chaos in Dallas as 11 officers are shot
Now Playing Police: Suspect said he...
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Gunshots ring out in Dallas, officers killed
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Video from balcony shows Dallas shooting
People rally in Dallas, Texas, on Thursday, July 7, 2016 to protest the deaths of Alton Sterling and Philando Castile. Black motorist Philando Castile, 32, a school cafeteria worker, was shot at close range by a Minnesota cop and seen bleeding to death in a graphic video shot by his girlfriend that went viral Thursday, the second fatal police shooting to rock America in as many days. / AFP / Laura Buckman (Photo credit should read LAURA BUCKMAN/AFP/Getty Images)
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Dallas shooting witness: People were trampled
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Witness describes Dallas police officer getting shot
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Dallas shooting witness: I heard about 20 gunshots
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Dallas Witness: 'Complete pandemonium' after shooting
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Disturbance in Dallas sends people running
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How police respond in 'active shooter' situations
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When can police shoot?
TOPSHOT - Bystanders stand near pollice baracades following the sniper shooting in Dallas on July 7, 2016. A fourth police officer was killed and two suspected snipers were in custody after a protest late Thursday against police brutality in Dallas, authorities said. One suspect had turned himself in and another who was in a shootout with SWAT officers was also in custody, the Dallas Police Department tweeted. / AFP / Laura Buckman (Photo credit should read LAURA BUCKMAN/AFP/Getty Images)
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Chaos in Dallas as 12 officers are shot
Law enforcement officials wait outside the emergency room entrance at Baylor University Medical Center.
Now Playing
Police: Suspect said he wanted to kill white officers
Bystanders stand near pollice baracades following the shootings.
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Shooting at Dallas protest in 60 seconds
A Dallas police officer, who did not want to be identified, takes a moment as she guards an intersection in the early morning after a shooting in downtown Dallas, Friday, July 8, 2016. At least two snipers opened fire on police officers during protests in Dallas on Thursday night; some of the officers were killed, police said.
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Desperate calls from Dallas officers during ambush
People rally in Dallas, Texas, on Thursday, July 7, 2016 to protest the deaths of Alton Sterling and Philando Castile. Black motorist Philando Castile, 32, a school cafeteria worker, was shot at close range by a Minnesota cop and seen bleeding to death in a graphic video shot by his girlfriend that went viral Thursday, the second fatal police shooting to rock America in as many days. / AFP / Laura Buckman (Photo credit should read LAURA BUCKMAN/AFP/Getty Images)
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'It looked like an execution'
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See video of Dallas shooting
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President Obama reacts to Dallas shootings from Warsaw
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Police: Suspect said he's going to kill more
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01:17
Gunshots ring out in Dallas, officers killed
01:23
Video from balcony shows Dallas shooting
People rally in Dallas, Texas, on Thursday, July 7, 2016 to protest the deaths of Alton Sterling and Philando Castile. Black motorist Philando Castile, 32, a school cafeteria worker, was shot at close range by a Minnesota cop and seen bleeding to death in a graphic video shot by his girlfriend that went viral Thursday, the second fatal police shooting to rock America in as many days. / AFP / Laura Buckman (Photo credit should read LAURA BUCKMAN/AFP/Getty Images)
01:03
Dallas shooting witness: People were trampled
01:10
Witness describes Dallas police officer getting shot
police officers shot dallas texas witness sot ctn_00010002.jpg
02:28
Dallas shooting witness: I heard about 20 gunshots
tx shooter witness_00000000.jpg
00:56
Dallas Witness: 'Complete pandemonium' after shooting
01:32
Disturbance in Dallas sends people running
active shooter police training orig_00004326.jpg
02:20
How police respond in 'active shooter' situations
01:55
When can police shoot?
TOPSHOT - Bystanders stand near pollice baracades following the sniper shooting in Dallas on July 7, 2016. A fourth police officer was killed and two suspected snipers were in custody after a protest late Thursday against police brutality in Dallas, authorities said. One suspect had turned himself in and another who was in a shootout with SWAT officers was also in custody, the Dallas Police Department tweeted. / AFP / Laura Buckman (Photo credit should read LAURA BUCKMAN/AFP/Getty Images)
02:16
Chaos in Dallas as 12 officers are shot
Law enforcement officials wait outside the emergency room entrance at Baylor University Medical Center.
02:26
Police: Suspect said he wanted to kill white officers
Bystanders stand near pollice baracades following the shootings.
01:09
Shooting at Dallas protest in 60 seconds
A Dallas police officer, who did not want to be identified, takes a moment as she guards an intersection in the early morning after a shooting in downtown Dallas, Friday, July 8, 2016. At least two snipers opened fire on police officers during protests in Dallas on Thursday night; some of the officers were killed, police said.
00:47
Desperate calls from Dallas officers during ambush
People rally in Dallas, Texas, on Thursday, July 7, 2016 to protest the deaths of Alton Sterling and Philando Castile. Black motorist Philando Castile, 32, a school cafeteria worker, was shot at close range by a Minnesota cop and seen bleeding to death in a graphic video shot by his girlfriend that went viral Thursday, the second fatal police shooting to rock America in as many days. / AFP / Laura Buckman (Photo credit should read LAURA BUCKMAN/AFP/Getty Images)
01:13
'It looked like an execution'
dallas police officer shooting ground vo_00003228.jpg
02:38
See video of Dallas shooting
president obama reacts to dallas shootings from warsaw poland_00000000.jpg
02:32
President Obama reacts to Dallas shootings from Warsaw
dallas police shooting chief david brown negotiating with suspect sot_00001104.jpg
00:59
Police: Suspect said he's going to kill more
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01:17
Gunshots ring out in Dallas, officers killed
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Story highlights
"Americans ... are feeling a sense of helplessness," attorney general says
Micah Xavier Johnson identified as dead gunman, law enforcement sources say
(CNN) — The ambush began with gunshots that killed five officers and sent screaming crowds scrambling for cover. It ended when a Dallas police bomb squad robot killed a gunman after negotiations failed.
Investigators have identified the dead suspect: 25-year-old Micah Xavier Johnson of Mesquite, Texas. But they're still trying to answer key questions. Chief among them: Was anyone else involved in the shootings, which began Thursday night during a protest against police violence and left parts of downtown Dallas under siege for hours? And are other suspects on the loose?
The deadly gunfire erupted in Dallas as videos showing two African-American men shot by police in Louisiana and Minnesota spurred protests and debate over police use of force across the country.
Officers shot during Dallas protest
Photos: Officers shot during Dallas protest
Two officers crouch behind barriers.
Dallas police order people away from the area after the shootings.
Police and others gather at the emergency entrance to the Baylor University Medical Center.
Police stop a driver in downtown Dallas.
A view of downtown Dallas after the shootings. Kent Giles captured the image and told CNN he "heard multiple shots being fired. Probably more than 20 rounds. This is the intersection of Main and Griffin looking towards the west."
Dallas police check a car after detaining a driver.
Dallas police stand watch after the shootings.
Onlookers stand near police barricades after the shootings.
Police attempt to calm the crowd after an arrest.
A clerk looks at broken windows that were shot out at a store in downtown Dallas.
Law enforcement officials wait outside the emergency room entrance of the Baylor University Medical Center.
Police respond after shots were fired in downtown Dallas on Thursday, July 7. <a href="
http://www.cnn.com/2016/07/08/us/philando-castile-alton-sterling-protests/index.html" target="_blank">Five police officers were fatally shot </a>during a protest over recent police shootings in Louisiana and Minnesota. Seven other officers were injured in the ambush, as were two civilians.
Emergency responders administer CPR to an unknown patient near the receiving area of the Baylor University Medical Center.
A police officer with Dallas Area Rapid Transit is comforted at the emergency room entrance of the hospital.
A police helicopter flies over the scene in downtown Dallas. One suspect was killed by police after a standoff that lasted for hours.
A man raises his hands as he walks near a law enforcement officer in Dallas.
Protesters gather as police officers arrest someone in the aftermath of the shootings.
A Dallas police officer takes a moment as she guards an intersection in the early morning hours.
Dallas police respond to the scene of the shootings.
Police officers shield bystanders after shots were fired at the protest.
Police officers take cover as shots are fired.
Police get in position after gunshots rang out.
Two officers crouch behind barriers.
Dallas police order people away from the area after the shootings.
Police and others gather at the emergency entrance to the Baylor University Medical Center.
Police stop a driver in downtown Dallas.
A view of downtown Dallas after the shootings. Kent Giles captured the image and told CNN he "heard multiple shots being fired. Probably more than 20 rounds. This is the intersection of Main and Griffin looking towards the west."
Dallas police check a car after detaining a driver.
Dallas police stand watch after the shootings.
Onlookers stand near police barricades after the shootings.
Police attempt to calm the crowd after an arrest.
A clerk looks at broken windows that were shot out at a store in downtown Dallas.
Law enforcement officials wait outside the emergency room entrance of the Baylor University Medical Center.
Police respond after shots were fired in downtown Dallas on Thursday, July 7. <a href="
http://www.cnn.com/2016/07/08/us/philando-castile-alton-sterling-protests/index.html" target="_blank">Five police officers were fatally shot </a>during a protest over recent police shootings in Louisiana and Minnesota. Seven other officers were injured in the ambush, as were two civilians.
Emergency responders administer CPR to an unknown patient near the receiving area of the Baylor University Medical Center.
A police officer with Dallas Area Rapid Transit is comforted at the emergency room entrance of the hospital.
A police helicopter flies over the scene in downtown Dallas. One suspect was killed by police after a standoff that lasted for hours.
A man raises his hands as he walks near a law enforcement officer in Dallas.
Protesters gather as police officers arrest someone in the aftermath of the shootings.
A Dallas police officer takes a moment as she guards an intersection in the early morning hours.
Dallas police respond to the scene of the shootings.
Police officers shield bystanders after shots were fired at the protest.
Police officers take cover as shots are fired.
Police get in position after gunshots rang out.
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Five police officers were killed and seven others were injured in the ambush. It was the deadliest single incident for U.S. law enforcement since September 11, 2001. Two civilians also were injured in the shootings, the Dallas mayor's office said.
As officials condemned the attack Friday, details emerged about the suspect who died after a lengthy standoff with police in a parking garage.
The suspect told police negotiators that he was upset about recent police shootings, that he wanted to kill white people -- especially white officers -- and that he acted alone, the city's police chief told reporters Friday.
"We saw no other option but to use our bomb robot and place a device on its extension for it to detonate where the suspect was," Chief David Brown said. "Other options would have exposed our officers to grave danger. The suspect is deceased as a result of detonating the bomb."
Law enforcement sources familiar with the investigation told CNN that Johnson was the dead gunman. He had no criminal record or known terror ties, a law enforcement official said.
He had served in the U.S. Army Reserve, training as a carpentry and masonry specialist, two U.S. defense officials said.
Wayne Bynoe, a neighbor, said police cars were outside Johnson's home Friday. Johnson lived with his mother and "keeps to himself," Bynoe said.
The Dallas police chief told reporters it's too soon to speculate on the suspect's motives, and it's unclear whether more suspects are on the loose.
"We're hurting. Our profession is hurting. There are no words to describe the atrocity that happened in our city," he said. "All I know is that this must stop -- this divisiveness between our police and our citizens."
U.S. Attorney General Loretta Lynch described the Dallas shootings as the latest in a series of tragedies that have left the country reeling.
"After the events of this week, Americans across the county are feeling a sense of helplessness, of uncertainty and of fear. Now, these feelings are understandable and they are justified," she said, "but the answer must not be violence."
The attack
Witnesses said protesters were marching peacefully in downtown Dallas when the gunfire started Thursday night.
The Rev. Jeff Hood, one of the protest organizers, said he saw two officers go down, then watched a sergeant running toward the gunfire.
"I ran the opposite direction. I was concerned about the 700 or 800 people behind me," he said. "I was screaming, 'Run! Run! Active shooter! Run!' And I was trying to get folks out as fast as I could."
Crowds ran into a parking garage, witnesses said, and spilled out after word spread a sniper was nearby.
"Everyone was screaming, people were running," said witness Clarissa Myles. "I saw at least probably 30 shots go off."
Police have said at least two snipers fired "ambush-style" from an "elevated position." Then police exchanged gunfire and negotiated with a suspect for hours at a parking garage in downtown Dallas.
Before authorities killed him with an explosive, the suspect told negotiators more officers were going to get hurt, and that bombs had been planted all over downtown.
Police found no explosives during sweeps of the area, Dallas police Maj. Max Geron said Friday morning on Twitter.
The victims
Police have said at least 10 officers were shot by a sniper, and that one officer was shot in a shootout at the parking garage. It's not clear where the 12th officer was shot.
Most of the injured officers have been released from the hospital, Brown told reporters. Their conditions are improving, Brown said, calling for the community to support them.
"We don't feel much support most days. Let's not make today most days," Brown said. "Please, we need your support to be able to protect you from men like these, who carried out this tragic, tragic event."
Dallas police Officer Patrick Zamarripa, a father of two, was one of the slain officers, according to social media posts from family members and reports from local media outlets. Military records show he was a U.S. Navy veteran who had been deployed to Bahrain as part of the Iraq War effort.
His brother shared a photo on Twitter with the caption: "Love you brother. Couldn't be prouder. We'll see you again. #PrayForDallas."