US military veteran expresses his indignation about recent police shootings by killing 5 white officers

The ambush began with gunshots that killed five officers and sent screaming crowds scrambling for cover. It ended when a Dallas police bomb squad robot killed a gunman after negotiations failed.

Investigators identified the dead suspect as 25-year-old Micah Xavier Johnson of Mesquite, Texas, a military veteran who'd served in Afghanistan. Police said they searched his home Friday afternoon and found bomb-making materials, ballistic vests, rifles, ammunition and a personal journal of combat tactics. Investigators are analyzing information in the journal, a police statement said.

But authorities are still trying to answer key questions. Chief among them: Are any other suspects on the loose?

Federal law enforcement officials say they believe Johnson was the only shooter in the ambush that began Thursday night, according to law enforcement officials briefed by the Dallas police.

Dallas police Chief David Brown earlier suggested that other suspects played a role, too.

"Through our investigation of some of the suspects, it's revealed to us that this was a well-planned, well-thought-out, evil tragedy by these suspects," Brown said at a prayer vigil for the victims Friday afternoon. "We won't rest until we bring everyone involved to justice."

The deadly gunfire erupted in Dallas after videos showing two African-American men shot by police in Louisiana and Minnesota spurred protests and debate over police use of force across the country.

Five police officers were killed and seven others were wounded in the ambush. It was the deadliest single incident for U.S. law enforcement since September 11, 2001. Two civilians also were hurt in the shootings, the Dallas mayor's office said.

As officials condemned the attack Friday, details emerged about the suspect who died after a lengthy standoff with police in a parking garage.

The suspect told police negotiators that he was upset about recent police shootings, that he wanted to kill white people -- especially white officers -- and that he acted alone, the city's police chief told reporters Friday.