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,

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.