WASHINGTON -- The Army said Friday that a suspect in the Dallas shooting served in the Army Reserve for six years and did a nine-month tour of duty in Afghanistan.

CBS News confirmed that the suspect has been identified as Micah Xavier Johnson, 25. Johnson was killed by a robot-delivered bomb in a standoff with police in an El Centro College campus building where he had exchanged fire with officers.

Officials say they believe Johnson was the lone shooter. A law enforcement source told CBS News the suspect was armed with a SKS semi-automatic assault rifle and a handgun, CBS News senior investigative producer Pat Milton reports. The suspect also wore body armor, the source said.

Dallas police say they found bomb-making materials, ballistic vests, rifles, ammunition, and a personal journal of combat tactics Friday at Johnson's home in Mesquite, about 30 minutes east of Dallas. He is believed to have shared the home with family members.

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They say detectives are in the processing of analyzing the information contained in the journal.

Authorities apparently finished an initial search of the home Friday. Agents in Bureau of Alcohol, Tobacco, Firearms and Explosives vests were seen on Friday carrying out several bags.

The Army released a portion of Johnson's service record that said he enlisted in March 2009 and served in the Army Reserve until April 2015. After leaving the Army Reserve, he joined the Individual Ready Reserve. The IRR is where former active duty or reserve soldiers aren't required to train but are kept on Army personnel rolls with the potential of being called to duty. An IRR soldier can volunteer for short tours on active duty.

Johnson was a private first class and at the time he entered the Army gave his home of record as Mesquite, Texas, the Army said.

His military occupational specialty was carpentry and masonry, the Army said.

The Army said Johnson deployed to Afghanistan in November 2013 and returned in July 2014. For that he was given an Afghanistan Campaign Medal with campaign star. He also earned an Army Achievement Medal, an Army Service Ribbon and an Armed Forces Reserve Medal with "M'' Device, among other standard awards for service.

An Army reservist who served with Johnson told CBS News he was "quirky and funny," "quiet," "happy-go-lucky," and "kind of like a child at heart."

"He stayed with his little crowd of close friends and was more or less innocent," the reservist said.

He said Johnson was "very passive, actually."

"I mean I'm in complete disbelief that he would even be capable of such things," the reservist said.

The reservist said he didn't deploy with Johnson's company, but didn't believe they saw combat.

Police say Johnson, who was black, told authorities that he was upset over the police shootings of two black men earlier this week and wanted to exterminate whites, "especially white officers," officials said Friday.

The reservist said Johnson wasn't hostile and didn't seem to hate anyone when he served with him about four years ago. He said Johnson had friends who were white, Hispanic and Asian.

Johnson was known by his family and neighbors as an "Army strong" veteran who loved playground basketball back home in suburban Dallas. Dallas police say that people they interviewed have described him as a loner.

Micah Xavier Johnson, right, is seen in a photo obtained by CBS News.

Johnson graduated from John Horn High School in Mesquite, school district officials said.

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."

On Saturday, Johnson posted a video of people slaughtering dolphins to a Black Panther Facebook page.

"Look at the joy on their faces," Johnson wrote. "Why do so many whites (not all) enjoy killing and participating in the death of innocent beings?"

Johnson's Facebook page has since been taken down.

Israel Cooper, who knew Johnson, said he went by the name Xavier. Cooper said Johnson had a "cool vibe" and wasn't really political but did seem educated.

He said 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.'"