'He wrote a letter in his own blood': New details have emerged about the night of the Dallas police shootings

The man who killed five police officers during a Black Lives Matter demonstration in Dallas on Thursday had been plotting a much larger attack but "fast-tracked" his plans in the wake of police shootings in Louisiana and Minnesota, Dallas police chief David Brown told CNN on Sunday.

"Our search of his home, in which we found bomb-making materials and a journal, leads us to believe that the suspect had been practicing explosive detonations with materials large enough to have devastating effects on the city," Brown told "State of the Union" host Jake Tapper on Sunday morning.

Police released a statement on Friday confirming that they had found bomb-making materials, ballistic vests, rifles, ammunition, and a personal journal of combat tactics at the home of the gunman, 25-year-old Dallas resident Micah Johnson.

Brown added: "We believe the deaths in Minnesota and Louisiana fast-tracked his plans. He saw the protest in Dallas as an opportunity to begin wreaking havoc on officers. We're convinced the suspect had other plans. He thought that what he was doing was righteous, and that he was going to make law enforcement pay for what he saw as their efforts to punish people of color."

The suspect wrote the letters "RB" in his own blood on a wall near where he was eventually killed, Brown said, indicating that he was injured before he engaged in a standoff with police.

"We're still trying to decipher what those letters mean," Brown told CNN.

Johnson told police that he was "upset about Black Lives Matter" and that he "wanted to kill white people," Brown said in a press conference on Friday. He also requested a black negotiator during the standoff, and then didn't believe the negotiator was black "because of his expertise," Brown told CNN on Sunday.

Police killed Johnson using a robot-controlled bomb after hours of negotiations broke down during a standoff in a Dallas parking garage. The decision to kill Johnson using a bomb has been criticized, but Brown has insisted that officers on the scene "had no choice."

"There was no progress on the negotiations," Brown told CNN. "He [Johnson] was lying to us, playing games, singing, asking how many he 'got', saying he wanted to kill more. He seemed very much in control and very focused on hurting more officers, and without our actions he would have. So, in my mind, we had no choice."

He added: "It's not worth my time to debate that. We believe we saved lives by making this decision. I appreciate the critics, but they're not on the ground and their lives are not being put at risk."

Johnson had no criminal history and was not on any FBI watch lists, according to a statement the Dallas Police Department released Friday. Video released in the wake of the shootings of Johnson in action prompted military experts to examine the gunman's tactics, which appeared professional and rehearsed.

"We don't normally see this type of movement from criminal suspects," Brown told CNN. "The military style was a plan - he had practiced this. The military training he received did influence how he planned to do this."

The Army later confirmed that Johnson served as an enlisted soldier and served a tour of duty in Afghanistan. It said Johnson was trained in the Army reserves as a carpentry/masonry specialist. It was unclear what type of firearms training he had.

Johnson's Facebook page, which has since been taken down, seems to corroborate what Dallas Police Chief David Brown described about his anger toward white people.

The page featured images of Black Power, and the red, black and green flag sometimes known as the Black Liberation flag, according to Reuters. He appeared in his profile photo with a raised fist in a Black Power salute, and posted an angry rant against white people on July 2.

"Why do so many whites (not all) enjoy killing and participating in the death of innocent beings," Johnson wrote in the post in a Facebook group called Black Panther Party Mississippi. "Then they all stand around and smile while their picture is taken with a hung, burned and brutalized black person. They even go to our homeland and shoot our endangered wildlife for sport."

Johnson's murder of five police officers on Thursday was the deadliest day for US law enforcement since September 11, 2001. Even so, Brown told CNN, "The day after this incident occurred, every single person came to work."

"We're not perfect - there are cops who don't need to be cops," Brown said. "But I'm proud to be associated with these people. I stay humble."