Dallas CNN  — 

Dallas Police Chief David Brown gave an order to his SWAT team after a 45-minute gun battle and two hours of negotiating with a sniper targeting police officers.

He told them to come up with a creative plan to neutralize the suspect without putting another officer in the line of fire.

In the time it took Chief Brown to get back from updating the public about the ongoing battle, his officers had hatched a plan. It would keep them out of the line of fire and take out the suspect.

“They improvised this whole idea in about 15, 20 minutes – extraordinary,” Chief Brown says.

By the time the chief gave the go ahead, at least two officers had already been killed, and several more gravely wounded. Three more would later die from their injuries.

The sniper was targeting police officers, particularly white officers.

“He was basically lying to us, laughing at us, singing and asking, ‘How many did he get?’ and saying that ‘he wanted to kill more,’” Chief Brown told CNN’s Jake Tapper.

Chief Brown made the final call and carried out a plan law enforcement experts say they’ve never seen done by local officials: Use a robot and a pound of C-4 explosive to take the sniper out.

The fight against military trained sniper

A Northrop Grumman Remotec document shows the force it can grip.

Chief Brown says the robot was used in the building where Johnson was still sniping, intent on continuing to kill.

They’d had the robot for a long while. The Remotec Androx Mark V A-1, manufactured by Northrup Grumman, was purchased by the department in 2008. The robot, which cost $151,000, sustained minor damage to the extension arm and is still functional, the chief says.

Chief Brown says his officers were up against a military trained suspect holed up on the second floor of El Centro Community College building in downtown Dallas.

Eventually the robot was maneuvered behind a “brick wall” with the suspect on the other side, the chief says. The robot was carrying the one pound payload, ready to be detonated.

“A pound of C-4 runs about 20 dollars,” if bought in bulk, explosive expert Matt Barnett of Bonetti Explosives told CNN.

Barnett is not in law enforcement, but he’s licensed to dispose of unexploded ordinances and has been working with explosive materials since he was a child out in West Texas. He agreed to demonstrate what a pound of C-4 can do when detonated against a wall.

The role of the C-4

Explosive expert Matt Barnett holds a pound of C-4.

The C-4 would likely be placed as close to the wall by the robot as possible for full effect, and quietly moved behind the wall so the sniper wouldn’t notice. If the police could do that, they could likely take out their attacker.

“A pound of C-4 is a lot” if its detonated inside a building, Barnett says. “It can do a lot more damage to the human body in an enclosed space than outside in the open air.”

“There are two things that’ll kill you with explosives,” Barnett says. “You have over pressure and fragmentation.”

“Fragmentation is the one we worry about most and usually that’s the number one killer with explosives,” Barnett says. “The fragments becomes like little missiles.”

They can go through a human body like “butter,” he says.

Over pressure would burst blood vessels and make a person dazed and confused, Barnett explained. They may not appear to be injured at first. But inside they are bleeding out.

Barnett fashions a pound of C-4 into a ball, then a brick shape with his gloved hands and secured in onto a two-by-four to simulate the robotic arm. The C-4 is pushed snug up to the concrete. A charge is placed inside the soft C-4 brick.

CNN is not detailing the other key steps to achieve the desired explosion.

When the blast occurs, it pierces the relatively quiet 100-plus acres in West Texas where the demonstration was conducted. It can be felt from behind a car, and more than a football field away.

Part of the brick wall is pulverized into dust but some of it is still standing.