Killer deftly improvised during attack, police chief says

The suspect who killed five police officers in Dallas last week had prepared a larger assault on law enforcement, the city's police chief said on Sunday, citing evidence gathered from the killer's home that showed he had practiced with explosives.

"We're convinced that this suspect had other plans," Police Chief David Brown told CNN, adding that the recent deaths of African-Americans at the hands of police in Minnesota and Louisiana led the Texas shooter to "fast track" his plans.

Brown also vigorously defended his decision to use a bomb mounted on a robot to kill the gunman while he was holed up after killing the five officers.

He said he approved the plan to detonate a bomb with "about of pound" of C-4 explosives after two hours of fruitless talks with the suspect, who sang, laughed and taunted with police negotiators.

The sniper, Micah X. Johnson, a black U.S. military veteran of the Afghan war, said he wanted to "kill white people" following the fatal shootings of two black men by police in Louisiana and Minnesota, officials said.

His attack came on Thursday evening during a protest in downtown Dallas against the fatal shootings of African American men in Baton Rouge and a Minneapolis suburb.

The shooting spree amplified a turbulent week in the United States, as the issues of race, gun violence and use of lethal force by law enforcement again convulsed the nation.

Nearly two dozen law enforcement officers were injured and more than 100 protesters arrested in St. Paul, Minnesota, overnight as demonstrators blocked a major highway. Dozens of protesters were arrested overnight in Baton Rouge, Louisiana, and angry demonstraters marched from New York's City Hall to Times Square.

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.Police had expected the Dallas protesters to remain in one area of the city center, but demonstrators spontaneously decided to march in a different direction, Brown said.

Authorities believe the shooter drove until he was well ahead of the protesters, stopping where he saw an opportunity to take "high ground" in buildings, Brown said. Because police had not planned to close streets, officers became exposed when engaged in crowd control, Brown said.

Johnson's military training aided his ability to shoot and rapidly move to other positions to fire again, single-handedly "triangulating" his fire so that police at first believed their were multiple shooters.

"We don't normally see this kind of running and shooting from criminal suspects," Brown said.

Although police believe Johnson acted alone, "we still have not ruled out whether or not others were complicit," Brown said.

Brown also revealed in the CNN interview that Johnson wrote the letters "RB" in his own blood when engaged in a standoff with police, a mysterious clue that remains under investigation, the Dallas police chief said.

"He wrote some lettering in blood on the walls, which leads us to believe he was wounded on the way up the stairwell," Brown said, adding that police were trying to decipher what RB meant.

In taking personal responsibility for approving the plan in the aftermath of Thursday's attack, Brown said he was convinced the gunman would have sought to harm other police officers if he had hesitated to give the go-ahead.

"I approved it and would do it again if presented with same circumstances," Brown told CNN.