The U.S. military veteran who fatally shot five Dallas police officers in a racially charged attack last week was plotting a larger assault, authorities said, disclosing how he had taunted negotiators and written on a wall in his own blood before being killed.
Police also found evidence of bomb-making material "large enough to have devastating effects throughout" Texas and a journal full of "ramblings" during a search of the suspect's home in Mesquite, according to Brown.
The protest was among several demonstrations nationwide following the deaths of 32-year-old Philando Castile in suburban St. Paul and 37-year-old Alton Sterling in Baton Rouge, Louisiana.
The Dallas police chief defended the department's use of a robot-delivered bomb to kill the suspect in Thursday's shooting. They are still trying to find out what the letters stand for. "We're trying to figure out... what those initials mean". His six years in the Army Reserve, including a tour in Afghanistan, were "not what Micah thought it would be... what he thought the military represented, it just didn't live up to his expectations".
He said 11 officers fired weapons at Johnson and that two used the explosive device.
"They were in a funnel", the chief said of his officers. "And it ended up being a fatal funnel".
Dallas County Chief Executive Judge Clay Jenkins said Johnson had been planning and training, and took advantage of the protest because of the high police presence.
"He lied to us, he was playing games, laughing at us, singing, asking how many did he get", Brown said, saying "he seemed very much in control" and determined to hurt more officers.
Mawuli Davis, an African-American attorney and activist in Atlanta, said the unrest continues because there has been no serious dialogue about issues of race and policing.
"I approved it, and I'd do it again if presented with the same circumstances", he said, adding that he had no patience for a debate on whether using the robot presented an unwise escalation in police tactics.
"Whenever those of us who are concerned about failures of the criminal justice system attack police, you are doing a disservice to the cause", the United States' first black president told a news conference.
"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", he said. "You're taking advantage of an officer and you're ensuring that you're able to kill them through them either being vulnerable or through a complete surprise attack".
Two of the three detainees were subsequently released, including a woman who was running with people who were armed, Brown said. One man was charged with a misdemeanor because he was not legally allowed to carry a gun, the chief added, without elaborating.
During Thursday's demonstration, Johnson demonstrated an ability to improvise by "leapfrogging" ahead of marchers and choosing a number of optimal positions from which to open fire on police, Brown told CNN.
"So we can not let the actions of a few define all of us", Obama said from Warsaw, Poland, where he attended a North Atlantic Treaty Organisation summit.
Brown killed five police officers July 9 at the end of what had been a peaceful protest against recent shootings by police that led to the deaths of several black men.
San Antonio police say shots fired overnight near the department headquarters hit the building, but nobody was hurt. "We went to his home, we saw that there was bomb-making equipment later, so it was very important that we realize that he may not be bluffing".