The gunman who killed five police officers in Dallas was plotting larger attacks, Dallas Police Chief David Brown said Sunday, reports CNN.

"We're convinced that this suspect had other plans and thought that what he was doing was righteous and believed that he was going to target law enforcement - make us pay for what he sees as law enforcement's efforts to punish people of color," Brown said in an interview with CNN's Jake Tapper on "State of the Union."

Brown said police found bomb-making materials and a journal at the shooter's home that suggested he'd been practicing detonations and appeared ready to take aim at larger targets.

He said the shooter, Micah Johnson, "obviously had some delusion. There was quite a bit of rambling in the journal that's hard to decipher."

Among Dallas investigators' current goals: Figure out what Johnson had meant by "RB," lettering that Brown said he'd written on the wall in blood before his death.

Police are "trying to figure out what those initials mean, but we haven't determined that yet," Brown said.

"At the scene where he was killed, he wrote some lettering in blood on the walls, which leads us to believe he was wounded on the way up the stairwell, on the second floor of the El Centro building and where we detonated the device to end the standoff there was more lettering written in his own blood," he said.

The details made for significant new disclosures about the killings that have rocked the Dallas community and the nation. Brown also sought to deliver a message to protesters in states like Minnesota and Louisiana after people there were killed by police last week in what critics have called cases of excess force.

"We're sworn to protect you and your right to protest, and we'll give our lives for it," Brown said.

"And it's sort of like being in a relationship where you love that person, but that person can't express or show you love back," he said. "I don't know if you've been in a relationship like that before, Jake, but that's a tough relationship to be in, where we show our love -- because there's no greater love than to give your life for someone, and that's what we're continuing to be willing to do."