Four and a half hours of terror

1 After two hours of a peaceful protest march, shots are fired from above at about 9 p.m. local time and the roughly 800 marchers scatter.

2 Police and attacker exchange gunfire; the heaviest shooting occurred around El Centro College. A video shot from a nearby apartment shows a man with an assault-style rifle shooting an officer in the back at point-blank range. Police believe this gunman fled inside the college.

3 Three suspects were detained. At some point, police see two suspects with a camouflage bag climb into a black Mercedes and speed off. They were stopped in the Oak Cliff neighborhood. A third suspect, a woman, was arrested near the El Centro garage.

4 At the college, a gunman kept SWAT officers at bay for three hours, during which he told a hostage negotiator that he wanted to kill white people. According to a college spokeswoman, the gunman apparently entered through broken windows or entrances in A Building , took stairs to the second floor of B Building and crossed to C Building . About 1:26 a.m., a loud blast was reported. Police said Micah Xavier Johnson, 25, died on the second floor of C Building after police detonated a bomb attached to a robot.

Large wheels and tracks allow navigation of steep slopes and

Extendable arm is capable of lifting 60 pounds fully extended and 145 pounds when retracted

Robots have carried explosives to breach doors or clear obstacles, but experts say this may be the first time a robot was used by police to kill a suspect. Dallas Police Chief David Brown said officers sent in the robot after hours of negotiations had failed. The device was a remote-controlled robot made by Northrup Grumman, specifically a Remotec Andros Mark V-A1. The department bought it in 2008 for about $151,000. Police placed a pound of C-4 explosive and detonation cord on its extension arm, and two officers operated it.

Johnson was an Army reservist who deployed to Afghanistan in 2013. During negotiations, Johnson told authorities he “wanted to kill white people, especially white officers,” Dallas Police Chief David Brown said. His Facebook page shows Johnson raising a single fist in the air, a symbol associated with the Black Power movement of the 1960s. Dallas police said a search of Johnson’s Mesquite, Texas, home revealed ”bomb-making materials, ballistic vests, rifles, ammunition, and a personal journal of combat tactics.”

The shooter was ‘upset about the recent police shootings’

Six officers in Texas have been shot and killed in 2016

Twenty-six officers have been killed in firearms-related incidents so far this year, including the five killed in the Dallas attack. This represents a 44 percent increase over the same time in 2015, a spokesperson for the National Law Enforcement Officers Memorial Fund said.

1 2 3 6 WA ME MT ND OR MN MA ID WI NY SD WY MI PA IA NE NV OH IN IL UT CO WV CA VA MD KS MO KY NC TN OK AZ AR NM SC AL GA MS LA AK TX FL 1 2 3 6 WA ME MT ND OR MN MA ID WI NY SD WY MI PA IA NE NV OH IN IL UT CO WV CA VA MD KS MO KY NC TN OK AZ AR NM SC AL GA MS LA AK TX FL

Update: A previous version of this map also included officer deaths from traffic-related and other causes.

[Obama calls Dallas shootings ‘a vicious, calculated and despicable attack’]