Sources: Dallas Shooting Suspect Had Been Planning An Attack; 5 Officers Dead, 7 Wounded

DALLAS (CBSNewYork/AP) -- A possible motive has been revealed in the attack that killed five police officers in Dallas Thursday night, and sources said the gunman is believed to have acted alone.

Dallas Mayor Mike Rawlings said Micah Xavier Johnson, 25, of Mesquite, Texas, acted alone in the shooting rampage that killed five officers and wounded seven more, CBS News' Danielle Nottingham reported.

"Mr. Johnson, now deceased, was the lone shooter in this incident," Rawlings said.

Police initially had believed there had been more than one sniper, but sources said the ricochet of bullets had made it sound like more shooters were involved, sources said.

"We believe now the city is safe, the suspect is dead, and we can move on to healing," Rawlings said.

As Jeff Paul of KTVT-TV, CBS11 in Dallas-Fort Worth reported, crews searched Johnson's home Friday and recovered bags full of evidence. Dallas Police said the suspect had materials to make bombs and a journal of combat tactics at his home.

Meanwhile, Dallas Police Chief David Brown reported that Johnson said he was upset over recent police shootings of black men and wanted to kill white people.

At a news conference Friday, Brown said the suspect made the comments before he was killed during a standoff with police in a downtown Dallas parking garage.

"There are no words to describe the atrocity that occurred to our city," Brown said.

A U.S. intelligence source further told CBS News that Johnson had been planning to do something for a while – though it is not clear exactly how long. Law enforcement will check where and when he bought his guns, vest, and bomb-making material to determine how long he has been planning an attack.

The source said the police shootings this week were the trigger for Johnson to commit the massacre, and the march was the opportunity.

"This was a well-planned, well thought-out, evil strategy," Brown said.

The Army said Johnson served from March 2009 to April 2015 in the Army Reserve and did one tour of duty in Afghanistan. It said Johnson was a private first class and his military occupational specialty was carpentry and masonry.

A law enforcement source tells CBS News that Johnson had an SKS semi-automatic assault rifle and a handgun. He also wore body armor. The SKS was originally manufactured in the Soviet Union but is popular with many gun enthusiasts around the world.

Investigators believe Johnson had sympathies with black separatist movements, but they have found no links to international or domestic terrorism groups. The investigation is fluid and ongoing, investigators said.

MORE: CBS DFW | CBSN | Photos: Attack On Police In Dallas

"We cornered one suspect and we tried to negotiate for several hours," Brown said. "Negotiations broke down, we had an exchange of gunfire with the suspect."

He said the suspect was upset about the Black Lives Matter movement and the recent police shootings.

"The suspect said he was upset at white people. The suspect stated he wanted to kill white people, especially white officers," Brown said.

The suspect also said that there were explosive devices planted around the city.

"The suspect stated that we will eventually find the IEDs," Brown said. "The suspect stated he was not affiliated with any groups and he stated that he did this alone."

Brown said his department used a robot-delivered bomb to kill the suspect after hours of negotiations failed.

"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," Brown said. "Other options would've exposed our officers to grave danger."

Police said that no explosives were found after extensive sweeps of downtown areas.

Three others were taken into custody, including a woman near the scene and two during a traffic stop, authorities said. But sources later said the others who were apprehended were not believed to be connected to the shooting.

"We're not going to be satisfied until every lead is exhausted, so if there's someone out there that was associated with this we will find you, and we will prosecute you, and we will bring you to justice," he said.

A robotics expert said Dallas police appear to be the first law enforcement agency to use a robot to kill.

'A Devastating Night'

The chaos began Thursday night when authorities said a sniper opened fire on police officers during a peaceful protest in downtown Dallas over the recent fatal shootings of black men by police – Alton Sterling in Baton Rouge, Louisiana and Philando Castile in Falcon Heights, Minnesota.

The protest was just ending before 9 p.m. Central Time Thursday when the shots rang out.

After the bedlam, Brown commended the actions of his officers in light of the direct attack on them.

"You'll see video footage of them running toward gunfire from an elevated position, with no chance to protect themselves, and to put themselves in harm's way to make sure citizens can get to a place of security," Brown said.

In reporting on Twitter that the fifth officer had died earlier Friday morning, the Dallas Police Department called it "a devastating night."

Dallas Mayor Mike Rawlings said Friday that two civilians were also hurt.

Thursday's shootings occurred only a few blocks from Dealey Plaza, the landmark made famous by the assassination of President John F. Kennedy.

Dozens of rounds were unleashed during the unprecedented assault.

"We got a guy with a long rifle but we don't know where the hell he's at," an officer could be heard saying over the police scanner.

People marching at the rally stopped walking to run for their lives.

"I was screaming, 'Run, run, run! Active shooter, active shooter!"' rally organizer Rev. Dr. Jeff Hood said.

The sniper shot down at the officers from an "elevated position," Brown said in an earlier statement. He raised the question of how the sniper -- or what at the time was believed to be more than one sniper -- knew the route of the protest for positioning purposes.

"They planned to injure and kill as many law enforcement officers as they could," Brown said.

After the shootings, police released a photo on Twitter of a man who they said was a person of interest who was wearing camouflage and had a rifle strapped over his shoulder.

The man, Mark Hughes – the brother of protest organizer Cory Hughes – later turned himself in to police. After being questioned, he was released.

Hughes told KTVT-TV that he "flagged down a police officer'' immediately after finding out he was a suspect. He says police lied during a 30-minute interrogation, telling him they had video of him shooting.

Videos posted online show Hughes walking around peacefully during the shooting and later turning over his gun to a police officer. Cory Hughes told KTVT-TV at the scene that he instructed his brother to hand over is gun – which he was carrying openly and legally – when the shots rang out.

Law Enforcement's Deadliest Day Since 9/11

Meanwhile, a memorial group said the slaying of the five officers was the deadliest day in U.S. law enforcement history since the Sept. 11, 2001, terrorist attacks.

Late Friday, the Texas Honor Guard carried out the heavy duty of escorting the bodies of the five officers who were killed to funeral homes. As CBS2's Valerie Castro reported, it was a sign of the solemn mood that had fallen over the Lone Star State.

Among the dead is 43-year-old Brent Thompson, an officer with Dallas Area Rapid Transit. DART said early Friday morning that Thompson joined the DART Police Department in 2009.

"Well-respected and well-liked -- he was a good officer he'd been married recently, just within the past month, I believe," said DART assistant vice president for external relations Morgan Lyons.

DART said he's the first officer killed in the line of duty since the agency formed a police department in 1989. The statement says "our hearts are broken.''

"This is something that touches every part of our organization," DART said. "We have received countless expressions of support and sympathy from around the world through the evening. We are grateful for every message."

Another victim, Officer Patrick Zamarripa, 32, was a veteran of three tours in Iraq.

"My son paid the ultimate price to take care of people," said the officer's father, Rick Zamarripa.

Rick Zamarripa talked with Scott Pelley on the CBS Evening News about his son. Patrick Zamarripa served three tours of duty in Iraq for the Navy before joining the Dallas police force.

"He was a good young man. He was my boy," Rick Zamarippa said. "The world lost but not as much as his daughter and his wife."

Dallas Police Senior Corporal Lorne Ahrens was a father and was married to a Dallas police detective.

Sgt. Michael Smith was the father of two teenage daughters.

Officer Michael Krol was living out his lifelong dream to serve as a police officer.

DART said the other three DART police officers shot during the protest are expected to recover from their injuries.

The four others killed during the shootings were Dallas police officers. CBS Dallas posted an image of officers saluting their fallen comrades as their bodies were being transported from the hospital.

Richard McBride's daughter, Misty McBride, was one of the officers who survived.

"She got shot, she fell over and turned around and started crawling back toward the car," he said.

A prayer was answered for Officer McBride's daughter, KTVT-TV's Dan Haggerty reported.

"I said that I love you and I'm glad that you're here," said Hunter McBride, 10.

The injured are all expected to pull through, and some already had been released from the hospital late Friday.

Meanwhile, a law enforcement source told CBS News that monitoring of social media overnight Thursday into Friday indicated an increase of threats to police online with one post saying "kill cops," CBS News senior investigative producer Pat Milton reported.

Calls For Calm

The White House announced Friday evening that President Barack Obama will visit Dallas early next week.

Meanwhile, speaking at a news conference Friday afternoon, U.S. Attorney General Loretta Lynch called the police shootings "an unfathomable tragedy'' in a week of "profound heartbreak and loss,'' but said violence is not the answer.

"After the events of this week, Americans across the county are feeling a sense of helplessness, of uncertainty and of fear," she said. "These feelings are understandable and they are justified. But the answer must not be violence. The answer is never violence."

Lynch said the spate of violence can't be allowed to "precipitate a new normal.''

"Rather, the answer must be action: calm, peaceful, collaborative and determined action," she said. "We must continue working to build trust between communities and law enforcement."

She said those concerned about suspect killings by police should not be discouraged "by those who use your lawful actions as a cover for their heinous violence.''

"I ask you to turn to each other, not against each other as we move forward," she said. "Let us support one another. Let us help heal one another."

In Dallas earlier Friday, Brown said his department and their families are grieving and that the divisiveness between police and the public must stop.

"Police officers are guardians of this great democracy: the freedom to protest, the freedom to speech, the freedom of expression. All freedoms we fight for with our lives. It's what makes us who we are as Americans. We risk our lives for those rights," he said. "We had an adequate amount of officers at this scene. We were blocking traffic and doing all the things to protect the people's right to protest and their free speech. We are not going to let a coward who would ambush police officers change our democracy, we're not going to do it. Our city, our country is better than that."

He said police "don't feel support" most days.

"Let's not make today most days," he said. "Please, we need your support to be able to protect you from men like these."

Police believe the sniper was aiming at officers as retaliation over the controversial police shooting deaths of Castile, 32, and Sterling, 37.

Castile was killed during a routine traffic stop outside of Saint Paul, Minnesota. The aftermath was captured and streamed live on Facebook by his girlfriend.

And in Baton Rouge, Louisiana, police officers shot and killed Sterling in a convenience store parking lot where he was selling DVDs, which was also captured on cell phone video.

The protests in Dallas were one of several held across the nation Thursday night, including in New York, Chicago, Philadelphia, Washington, D.C., Miami, Baton Rouge and other cities.

President Obama, speaking from Warsaw, Poland where he was meeting with leaders of the European Union and attending a NATO summit, said American is "horrified" over the shootings.

"We stand united with the people and the police department in Dallas," he said. "There is no possible justification for these kinds of attacks or any violence against law enforcement."

He said justice will be done and he's asking all Americans to pray for the fallen officers and their families.

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