In his final moments, Dallas suspect apparently tried scrawling message on wall

"As a policing family here in Dallas and across the country, there is a heightened sense of awareness around threats we received all over the country", he said.

A woman walks her dog past the home where Micah Johnson, the gunman who killed several police officers at a protest march, lived with his mother Saturday, July 9, 2016, in Mesquite, Texas.

During negotiations, Brown said Johnson asked how many officers were killed.

Both parents agreed their son never showed any outward signs of hatred for white people, indeed Johnson's stepmother, Donna, is white.

Johnson, an Army veteran, scrawled a message in blood on a parking garage wall before police killed him with a bomb-toting robot.

Obama, while saying there was a "persistent problem of African-Americans and Latinos being treated differently in our criminal justice system", stressed he did not believe the country was descending into the polarization seen in the sometimes violent civil rights struggles of the 1960s.

The deaths in Baton Rouge and St. Paul were the latest in a series of high-profile and controversial killings of black men by police in cities including New York, Ferguson, Missouri, Chicago and Baltimore.

The additional details of Johnson's behavior came after a tense night marked by the arrest of a prominent activist in the Black Lives Matter movement and protests in Louisiana and Minnesota that resulted in as many as 200 arrests, according to activists and police.

Authorities have said Johnson had plans for a larger assault, possessed enough explosive material to inflict far greater harm and kept a journal of combat tactics.

The bomb technician said the gunman wasn't a novice and "knew what he was doing", Brown told reporters today.

The robot, which was attached to about a pound of C4 explosive, likely saved more police officers from being killed, Brown said.

"I approved it and would do it again if presented with same circumstances", Brown told CNN on Sunday, referring to the strategy of deploying a bomb-equipped robot into a room where the suspect was holed up after his shooting rampage. "Serve your community", Brown said at a news conference yesterday. "We are all on edge and being very careful", he said.

A source said: 'There's lots of possibilities but RBG makes the most sense given Johnson's Black Power interests and what motivated him to carry out these attacks.

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