DALLAS --An Army veteran killed by Dallas police after the sniper slayings of five officers amassed a personal arsenal at his suburban home, including bomb-making materials, bulletproof vests, rifles, ammunition and a journal of combat tactics, authorities said Friday.
Homeland Security Secretary Jeh Johnson said Friday afternoon that the mass shooting was the work of "one gunman with no known links to or inspiration from any international terrorist organization," ABC News reports.
PHOTOS: Shots fired during Dallas protest
The man identified as 25-year-old Micah Johnson told authorities he was upset about the police shootings of two black men earlier this week and wanted to exterminate whites, "especially white officers," officials said.
He was killed by a robot-delivered bomb after the shootings, which marked the deadliest day for U.S. law enforcement since the Sept. 11, 2001, terrorist attacks. In all, 12 officers were shot.
In Georgia, Missouri and Tennessee, authorities said gun-wielding civilians also shot officers in individual attacks that came after the two black men died at the hands of police in Louisiana and Minnesota. Two officers were wounded, one critically.
President Barack Obama and Texas Gov. Greg Abbott asked for the public's prayers. In a letter posted online Friday, Abbott said "every life matters" and urged Texans to come together.
"In the end," he wrote, "evil always fails."
Johnson was a private first class from the Dallas suburb of Mesquite with a specialty in carpentry and masonry. He served in the Army Reserve for six years starting in 2009 and did one tour in Afghanistan from November 2013 to July 2014, the military said.
After the attack, he tried to take refuge in a parking garage and exchanged gunfire with police, Police Chief David Brown said.
The suspect described his motive during negotiations and said he acted alone and was not affiliated with any groups, Brown said.
Johnson was black. Law enforcement officials did not disclose the race of the dead officers.
Johnson's sister posted a note to the media and friends on her Facebook page Friday saying, "I keep saying its not true...my eyes hurt from crying. Y him??? And why was he downtown," Nicole Johnson wrote. "Please out of respect for my family. If you following the news and know whats going on. I'm not talking to anyone and please keep your comments thoughts respectful. The news will say what they think but those that knew him know this wasn't like him. Only close family can call me. This is the biggest loss we've had."
The bloodshed unfolded just a few blocks from where President John F. Kennedy was slain in 1963.
The shooting began Thursday evening while hundreds of people were gathered to protest the killings in Baton Rouge, Louisiana, and suburban St. Paul, Minnesota. Brown told reporters that snipers fired "ambush-style" on the officers. Two civilians also were wounded.
Authorities initially blamed multiple "snipers" for Thursday's attack, and at one point said three suspects were in custody. But by Thursday afternoon, all attention focused on Johnson, and Homeland Security Secretary Jeh Johnson said the entire attack appeared to be the work of a single gunman.
A Texas law enforcement official identified the man killed in the parking garage as Johnson. The official spoke on the condition of anonymity because he said he was not authorized to release the information.
Around midday, investigators were seen walking in and out of a home believed to be Johnson's in Mesquite.
In Washington, the nation's top law enforcement official, Attorney General Loretta Lynch, called for calm, saying the recent violence can't be allowed to "precipitate a new normal."
Lynch said protesters concerned about killings by police should not be discouraged "by those who use your lawful actions as a cover for their heinous violence."
The other attacks on police included a Georgia man who authorities said called 911 to report a break-in, then ambushed the officer who came to investigate. That sparked a shootout in which both the officer and suspect were wounded but expected to survive.
In suburban St. Louis, a motorist shot an officer at least once as the officer walked back to his car during a traffic stop, police said. The officer was hospitalized in critical condition.
And in Tennessee, a man accused of shooting indiscriminately at passing cars and police on a highway told investigators he was angry about police violence against African-Americans, authorities said.
Video from the Dallas scene showed protesters marching along a downtown street about half a mile from City Hall when shots erupted and the crowd scattered, seeking cover. Officers crouched beside vehicles, armored SWAT team vehicles arrived and a helicopter hovered overhead.
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Demonstrations were held in several other U.S. cities Thursday night to protest the police killings of two more black men: A Minnesota officer on Wednesday fatally shot Philando Castile while he was in a car with a woman and a child, and the shooting's aftermath was livestreamed in a widely shared Facebook video. A day earlier, Alton Sterling was shot in Louisiana after being pinned to the pavement by two white officers. That, too, was captured on a cellphone video.
The Dallas shootings occurred in an area of hotels, restaurants, businesses and some residential apartments only a few blocks from Dealey Plaza, the landmark made famous by the Kennedy assassination.
The scene was chaotic, with officers with automatic rifles on the street corners.
"Everyone just started running," Devante Odom, 21, told The Dallas Morning News. "We lost touch with two of our friends just trying to get out of there."
Carlos Harris, who lives downtown, told the newspaper that the shooters "were strategic. It was tap, tap, pause. Tap, tap, pause," he said.
Video posted on social media appeared to show a gunman at ground level exchanging fire with a police officer who was then felled.
Mayor Mike Rawlings said one of the wounded officers had a bullet go through his leg as three members of his squad were fatally shot around him.
"He felt that people don't understand the danger of dealing with a protest," said Rawlings, who spoke to the surviving officer. "And that's what I learned from this. We care so much about people protesting, and I think it's their rights. But how we handle it can do a lot of things. One of the things it can do is put our police officers in harm's way, and we have to be very careful about doing that."
Few details about the slain officers were immediately available.
Four of the dead were with the Dallas Police Department, a spokesman said. One was a Dallas Area Rapid Transit officer. The agency said in a statement that 43-year-old officer Brent Thompson, a newlywed whose bride also works for the police force, was the first officer killed in the line of duty since the agency formed a police department in 1989.
"Our hearts are broken," the statement said.
Theresa Williams said one of the wounded civilians was her sister, 37-year-old Shetamia Taylor, who was shot in the right calf. She threw herself over her four sons, ages 12 to 17, when the shooting began.
Other protests across the U.S. on Thursday were peaceful, including in New York, Atlanta, Chicago and Philadelphia. In Minnesota, where Castile was shot, hundreds of protesters marched in the rain from a vigil to the governor's official residence.
DETAILS EMERGE ON VETERAN LINKED TO DALLAS SNIPER SHOOTINGS
Micah Xavier Johnson was known by his family and neighbors as an "Army strong" veteran who served in Afghanistan and loved playground basketball back home in suburban Dallas.
He's now known more widely as the 25-year-old armed suspect killed Friday just hours after five police officers were fatally shot and seven wounded after a downtown demonstration.
Johnson was believed to have shared a two-story tan brick home in Mesquite, about 30 minutes east of Dallas, with family members. He graduated from John Horn High School in Mesquite, school district officials said.
He began serving the Army in March 2009, Army officials said. Johnson was a private first class with a military occupational specialty of carpentry and masonry. Toward the end of his tenure, Johnson was deployed to Afghanistan from November 2013 and returned in July 2014. His service ended in April 2015.
On what appears to be Johnson's Facebook page, photographs posted by someone who identified herself as a relative showed him in a U.S. Army uniform and holding an unknown object as though it were a weapon.
The relative also left a comment on his birthday in 2014 that called him "definitely Army strong" and an "entertaining, loving, understanding, not to mention handsome friend, brother (and) son."
The shootings began shortly before 9 p.m. Thursday when, police say, an uncertain number of snipers shot and killed five police officers, wounded seven more and injured two civilians. A demonstration to protest the recent killings of black men by police in Baton Rouge, Louisiana, and St. Paul, Minnesota, was wrapping up when gunfire erupted, police said.
Hours later, police cornered Johnson in a parking garage and began lengthy negotiations. After those failed, police used explosives delivered by a robot to "blast him out" and he died, said Dallas Mayor Mike Rawlings in a Friday morning news conference.
During those waning moments of Johnson's life, police say, he had told negotiators he was upset about recent police shootings and wanted to kill white people, particularly white officers.
Dallas Police Chief David O. Brown added in a news conference Friday that the suspect said he'd acted alone and was unaffiliated with any group, though it remains unclear whether that was the case. Brown said there were others in custody but he would not discuss the nature of those detentions. The chief added that police still didn't know if investigators had accounted for all participants in the attack.
After Johnson was killed, a relative posted onto her Facebook page, "I keep saying its not true...my eyes hurt from crying. Y him-? And why was he downtown." She did not respond to Facebook messages.
For several hours Friday morning, police blocked access to the home where Johnson was believed to have lived in Mesquite, a blue-collar suburb. Investigators in Bureau of Alcohol, Tobacco, Firearms and Explosives vests were seen carrying out several bags of material.
Just before noon Friday, officers stopped blocking the street in Mesquite. After that, no one answered a knock on the door.
Nearby, Israel Cooper said Johnson went by the name Xavier. Cooper says Johnson had a "cool vibe" and wasn't really political but did seem educated.
He says he played basketball with him at a park near the house. He says, "He would be out there for eight hours. Like it was his job. Just hoopin'."
Cooper said that when he heard the suspect was Johnson, he "was in disbelief because he's just not like a violent or rough dude."
"So I was, 'nah, it's probably another Xavier somewhere, you know,' " Cooper said. "But then, with pictures on the internet and stuff, I'm like 'OK.' "
Cooper added: "It's the quiet ones that just do the most devastating stuff. You never see it coming. But then it's more expected, like 'I should have known.'"