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The Dallas police chief on Monday defended his decision to use a bomb-strapped robot to kill the gunman suspected of fatally shooting five officers, insisting he would "use any tool necessary to save our officers' lives."

"I'd do it again," David Brown said, adding that the move "wasn't an ethical dilemma for me."

He said he advised those operating the robot after a two-hour standoff with the gunman, Micah Xavier Johnson, not to "bring the building down."

"That was the extent of my guidance," Brown said. The plan was devised in about 15 minutes, he said.

"We knew this was the suspect. He was asking us how many did he get," Brown said. "And he was telling us how many more he wanted to get."

At that point, it was unknown how many officers Johnson had injured. Later, the chief learned that five were killed and others were wounded. He said Monday that nine officers were injured in the ambush.

A policeman visits a makeshift memorial at the Dallas police headquarters, on July 11, 2016, in Dallas. Five police officers were killed and several injured uring a shooting in downtown Dallas last Thursday night. Eric Gay / AP

Eleven officers fired at Johnson, including one of the wounded, Brown said Monday. Two operated the explosive device that left Johnson dead after negotiations with him failed.

Brown said Sunday that the investigation into the shooting has revealed that Johnson had enough explosives in his home and knowledge to render "devastating effects throughout our city and our north Texas area."

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The investigation is now focused on cryptic letters Johnson wrote in his own blood — "RB" — in two areas of the building he had barricaded himself in after the shooting.

Related: Dallas Police Chief: Sniper Left Ominous Message Written in Blood, Planned Explosions

Detectives are also combing through 170 hours of body camera video from the scene of the shooting and reviewing statements from witnesses and officers to determine who should be questioned further to bring greater light to the attack, which Brown has said was a reaction to recent two police shootings of black men, Alton Sterling and Philando Castile.

Authorities have said that Johnson, an Army veteran, acted alone, but investigators are still working to make sure he didn't have help and no one else was aware of his plans.

"I'm highly protective of cops and I want to make sure there’s nobody else out there that had something to do with this," Brown said.

A Dallas Police Officers guards the scene of a shooting as investigators work in downtown Dallas, Friday, July 8, 2016. LM Otero / AP

Brown expressed repeatedly his dedication to his officers while speaking with reporters Monday. He said "my brain is fried" and "I'm running on fumes" in the wake of the carnage, but spoke clearly and passionately about his city and the men and women he oversees who work to keep it safe.

The department is hurting as officers deal with the investigation into the shooting, the policing responsibilities of the day-to-day and the upcoming services for those they lost.

Related: Dallas Shootings Took Heavy Toll on Officers of the Southwest Division

"It’s going to be the most challenging thing in my life," Brown said. "I don’t know how I’m going to do the rest of the week."

But "I'm a person of faith," Brown said. "I believe that I’m able to stand here is a testament to God’s grace and his sweet tender mercies, just to be quite honest with you."

“This tragedy … will not discourage us from changing and performing policing in America,” Brown vowed.

Brown’s resolve was lauded by the team at Parkland Trauma Center that treated seven of the injured officers Thursday night and expressed that even in their state of pain, they too, would not lose sight of their mission to care for the people of Dallas.

PHOTOS: Dallas Police Officers Killed in Protest Shootout

“I think the chief said it best this morning: We’re hurting we’re all hurting. This rocked some guys to their core who I thought were unshakable,” said Parkland’s Medical Director Dr. Alexander L. Eastman.

But “this city needs us to keep moving forward. This is a time for us to all come together,” Eastman said.

He said Dallas would use the situation for good and “people who never before talked to one another, or hugged one another — black, white, surgeon, not — we don’t care. … This city is going to come together and show the world exactly what we’re made of.”

Dr. Brian H. Williams, a staff surgeon who was working at Parkland Thursday night, echoed Eastman’s sentiment, saying the violence impacted him personally because, as a black man, “I understand the anger and the frustration and destruction of law enforcement.”

“But I abhor what has been done to these officers,” Williams said.

“Black men dying, people retaliating. We have to come together and end all this,” he said. “This killing it has to stop.”