Micah Johnson

The suspect in the deadly attack on Dallas police officers scrawled letters in his own blood on the walls of the parking garage where officers cornered and later killed him, the police chief said Sunday.

Police agencies across the U.S. are on edge and on guard after receiving threats and calls for violence against them on social media in the aftermath of the killings of two black men and the sniper attack that left five officers dead in Dallas. Some departments ordered officers to pair up or more generally said they were heightening security.

The gunman who killed five police officers at a protest march had practiced military-style drills in his yard and trained at a private self-defense school that teaches special tactics, including “shooting on the move,” a maneuver in which an attacker fires and changes position before firing again.

Can this really be America in 2016?

President Barack Obama said Saturday that the gunman responsible for killing five Dallas police officers was a “demented individual” who does not represent black Americans any more than a white man accused of killing blacks at a church in Charleston, South Carolina, represents whites.

The black Army veteran who killed five Dallas police officers donned a protective vest and used a military-style semi-automatic rifle in the sniper slayings, officials said, an attack that layered new anxiety onto a nation already divided about guns and how police treat African-Americans.

When Dallas police used a bomb-carrying robot to kill a sniper, they also kicked off an ethical debate about technology’s use as a crime-fighting weapon.

A black Army veteran upset about fatal police shootings of black men and bent on exterminating white police officers killed five lawmen in a sniper attack that layered new anxiety onto a nation already divided about guns and how police treat African-Americans.