Dallas Police Chief David Brown held a media briefing Monday morning to update several aspects of the investigation into the sniper attack that killed five officers Thursday.

Brown candidly spoke about the progress of the investigation, his personal reactions to the loss of five people dedicated to protecting the public, and had a message to protesters that have been critical of police handling of black people in recent weeks.

Full Coverage: Dallas Sniper Attack

A total of 13 officers engaged the shooter during the course of the evening - 11 who returned gunfire, and two officers who used the explosive device which ultimately killed the suspect.

Among the many questions Brown said still remain about the shooter and his motives is the meaning of the letters "RB," which were found written in blood by the suspect. Some have questioned whether the letters indicated an accomplice or larger network connected to the shooting.

Brown maintained it wasn't clear at this point what the letters meant, but that his department was "going to turn over every rock" until they are absolutely certain whether the shooter acted alone.

For the one man known to be responsible for the deaths of five officers, Brown said it was obvious "he thought what he was doing was righteous."

The department is currently reviewing more than 170 hours of body camera footage and talking to more than 300 witnesses as they piece together every detail of Thursday's events.

As the briefing went on, Brown touched on several points of frustration.

Chief Brown addressed the difficulty and confusion caused in the first moments of the attack by the number of weapons that were in the immediate area. As an open-carry state, there were several there who had weapons visible. He said that the open-carry law makes handling large events "increasingly difficult."

"We don't know who the good guy is versus who the bad guy if everybody starts shooting," he said.

Turning his attention to the protests which were the setting of the shooting, Brown was pointed in his criticism of the situation he says police are put in.

Brown mentioned that he and his family received death threats in the immediate aftermath of the attack. Tensions continued as on Saturday, shots were fired at the San Antonio Police headquarters, and the Dallas headquarters was subject to a threat that led to a SWAT presence that same day.

"We are asking cops to do too much in this country," he said. He stated that his officers are among the lowest-paid in the area, with starting salaries beginning at $44,000 a year. And for that amount, he says, officers are subject to an unfair amount of blame.

"Every societal failure, we put it off on the cops to solve. Mental health isn't getting enough funding - let's have the cops handle it," he said. "Not enough drug conviction busts... Loose dogs... Schools fail - give it to the cops. Policing was never meant to solve all those problems."

To the protesters themselves, Brown offered a simple solution as to how their concerns could be addressed.

"We're hiring. Get off the protest line and put in an application. If anything needs to be done, it needs to be done by our public," he said. "This democracy requires their participation."