Dallas police killed the suspect with a robot-delivered bomb after hours of overnight negotiations in a parking garage had failed. The law enforcement official spoke to the AP on the condition of anonymity because he said he was not authorized to release the information.

Dallas Police Chief David O. Brown said in a news conference earlier Friday that the suspect had told negotiators he was upset about recent police shootings and wanted to kill white people, particularly white officers. Brown did not name the suspect.

The suspect also told negotiators that he'd acted alone in the shooting and was unaffiliated with any group, Brown said, but it remains unclear whether that was the case. Brown said other suspects were in custody but would not discuss those detentions. Brown added that police still didn't know if investigators had accounted for all participants in the attack.

Thursday's fatal shooting began shortly before 9 p.m. when, police say, an uncertain number of snipers shot and killed five police officers, wounded seven more and injured two civilians at a downtown Dallas demonstration to protest the recent killings of black men by police in Baton Rouge, Louisiana, and St. Paul, Minnesota.

Little was immediately known about Johnson's life or motives. A check of a commercially driver's license listed an address for him in the Dallas suburb of Mesquite. Another person sharing his last name also was listed at that address, but it was immediately unclear whether they were related and still lived there.

On what appears to be Johnson's Facebook page, photographs posted by a relative show him in U.S. Army uniform and holding an unknown object as though it were a weapon.