The gunman who killed five Dallas police officers appeared to have been planning a larger attack, Dallas Police Chief David Brown said on Sunday, after a search of shooter Micah Johnson's home revealed bomb-making materials and a journal.
Meanwhile, protests around the U.S. against the shootings of two black men by police officers continued over the weekend.
Johnson was killed by police using a remote-controlled bomb on Thursday night, after shooting 12 police officers - five fatally - at the end of a protest march in the city's downtown area. The army veteran scrawled the letters "RB" on a wall in his own blood before dying, Brown revealed, according to reports of an interview the police chief gave to CNN on Sunday.
"We're trying to figure out through looking at things in his home what those initials mean," Brown said.
The police chief said that a search of Johnson's home revealedevidence of bomb-making materials and a journal that indicated the shooter had undertaken practice detonations, Brown told CNN.
"We are convinced that this suspect had other plans and thought that what he was doing was righteous and believed that he was going to make law enforcement... and target law enforcement... and make us pay for what he sees as law enforcement's effort to punish people of color," Brown told CNN's Jake Tapper.
Brown said that police believed the deaths of Alton Sterling and Philando Castile on Tuesday and Wednesday had caused 25-year-old Johnson to "fast track" his plans for an attack on police.
Meanwhile, the White House said President Barack Obama would travel to Dallas on Tuesday to deliver remarks at an interfaith memorial service at the Morton H. Meyerson Symphony Center. Obama will cut short a visit to Europe, where on Sunday he was meeting Spain's acting Prime Minister Mariano Rajoy and King Felip VI.
Speaking in Madrid, Spain, Obama said attacks on police over racial bias would hurt the Black Lives Matter (BLM) movement.
"Whenever those of us who're concerned about failures of the criminal justice system attack police, you're doing a disservice to the cause," the president said.
Protests against the shootings of two black men by police officers shut down main arteries in a number of U.S. cities on Saturday, leading to numerous arrests, scuffles and injuries in confrontations between police and demonstrators.
Undeterred by heightened concerns about safety at protests after Johnson killed five police officers in Dallas Thursday night, organizers went ahead with marches in the biggest metropolis, New York City, and Washington D.C., the nation's capital, among other cities.
Authorities in Baton Rouge say more than 100 people were jailed in connection with the Black Lives Matter protests held in the Louisiana city over the weekend.
Spokeswoman Casey Rayborn Hicks of the East Baton Rouge Sheriff's Office told Associated Press that more than 101 people were being held in the parish jail in connection with the protests, mostly for misdemeanors for not leaving a major thoroughfare known as Airline Highway.
Louisiana Governor John Bel Edwards said he was proud of how the police had handled the protests so far, saying law enforcement had responded in a "moderate" manner. He also said the vast majority of protesters had acted lawfully and nonviolently.
Edwards said, however: "It is not ... appropriate to allow them to simply block a major thoroughfare like Airline Highway."
Protesters from Louisiana or out of state will not be allowed "to incite hate and violence, to engage in unlawful activities," Edwards told a news conference. "Now, I want to be very clear. That will not be tolerated."
Among those arrested was DeRay Mckesson, who rose to prominence with the Black Lives Matter (BLM) movement after the 2014 shooting death of Michael Brown in Ferguson, Missouri. Mckesson was reportedly booked on a misdemeanor charge of obstructing the highway. NBC reported that Mckesson, who live-streamed his arrest on Periscope, was later released.
"The only people who were violent last night were the Baton Rouge Police department," Reuters reported that Mckesson told reporters after his release. "The protesters remained peaceful, both here and across the country."
It was the third straight day of widespread protests after the fatal shooting of Alton Sterling, 37, by police in Baton Rouge on Tuesday and the death of Philando Castile, 32, on Wednesday night in a St. Paul, Minnesota suburb, cities which both saw heated protests on Saturday.
The most recent shooting deaths by police come after several years of contentious killings by law enforcement officers, including that of Michael Brown, a teenager whose death in the summer of 2014 caused riots and weeks of protests in the St. Louis suburb of Ferguson.
On Saturday evening, hundreds of protesters shut down I-94, a major thoroughfare linking the Twin Cities, snarling traffic.
Protesters, told to disperse, threw rocks, bottles and construction rebar at officers, injuring at least three, St. Paul police said. Police said they made arrests and used smoke bombs and marking rounds to disperse the crowd. Protesters at the scene said police fired tear gas and rubber bullets.
The city's mayor and a protest leader both decried the violence, which injured 21 officers and led to 102 arrests. St. Paul police said one officer suffered a broken vertebrae when a concrete block was dropped on his head during the protest on the interstate.
"We will not tolerate the kind of shameless violence we saw throughout the course of the night," St. Paul Mayor Chris Coleman told a news conference. "This doesn't honor anyone's memory."
In St. Paul, Rashad Turner, leader of the local chapter of the Black Lives Matter group, told WCCO-TV that the throwing of rocks and bottles at officers was disturbing. He blamed outside agitators for the violence, not the protesters on the freeway.
"It's ridiculous. It cannot happen. It's not what we do here in St. Paul," Turner said. "It does not honor Philando Castile."
Authorities said 50 protesters were arrested on the Minnesota interstate and 52 others later on a street near the governor's mansion, the site of most of the protests since Castile was shot on Wednesday.
Police said early on Sunday they had begun clearing the highway of debris in preparation for re-opening it.
Protests also took place Saturday in Nashville, where protesters briefly blocked a road, and in Indianapolis. A rally in San Francisco also briefly blocked a freeway ramp, according to local media.
Hundreds of protesters marched from City Hall to Union Square in New York. The crowd swelled to around a thousand people, closing down Fifth Avenue. Some chanted "No racist police, no justice, no peace" as rain fell in New York.
"I'm feeling very haunted, very sad," said Lorena Ambrosio, 27, a Peruvian American and freelance artist, "and just angry that black bodies just keep piling and piling up."
New York police said they arrested about a dozen protesters for shutting down a major city highway.
- CNBC contributed to this report.