Transcript for How Bethany Mota turned her YouTube channel into a full-time career
At a time of so much tension between police and the African-American community, you're going to hear tonight from an unusual and powerful voice. He's not only a former police chief who knows what it's like to wear the badge, he's also a black man who lost his own son in a police shoot-out. Here's my "Nightline" coanchor Byron Pitts. Reporter: It's a narrative that keeps playing itself out over and over again. Hands up, don't shoot! Reporter: Unarmed black men fatally shot by white police officers. Oh, I shot him, I'm sorry. Reporter: Critics say too often those officers are cleared of all wrongdoing. Tulsa, Oklahoma. A police officer shot and killed 40-year-old Terence Crutcher last year. She told a jury she thought he was trying to see if he had a gun in his pocket or his truck. Reporter: She was acquitted three weeks ago, sparking protests. Officer Shelby's lawyer said today in a statement, she is still struggling with the ordeal of being charged with a crime for doing as her training provided and grieving the taking of another human life. This fits a narrative in America for many people that if you are black and male and you're dealing with a cop who's white, there's a chance you're not going to survive that. That's cherry picking what's happened in policing. It's not even accurate. Reporter: Former Dallas police chief David brown says it doesn't tell the whole story. You can choose to pick an equal amount of courageous, brave incidents where officers risk their lives to save people of color. And then that will be your narrative. Reporter: Early in his tenure as chief he says his city narrowly avoided a black versus blue moment that could have divided everyone. My nephew gets shot in the back! Reporter: It was the summer of 2012. A police officer shot a suspect. Right from the start, Keith brown knew there would be controversy. The suspect's black. He's unarmed. The officer's white. And there's rumors in the community immediately that the suspect was running away and the white officer shot him in the back. People wanted to believe it. Reporter: The chief called a press conference to get the facts out. He became fatigued and was losing the fight. Rumors were so strong, this community was so tight knit, whatever was said on the ground, if not corrected, would be the uth. Everything else afterwards would be a lie and not to be trusted. What if the facts in that case didn't land on the side in favor of law enforcement? Would you still have been so willing to give the information? Yes, because I have a number one principle. Be the first to say you're wrong. The issue is trust. Hard to earn. Easy to lose. And so I knew how fragile the situation was. Reporter: The situation that would ultimately define his career and shake the nation happened four years later. A day that haunts chief brown still. July 7th, the world changed. Yes. I had made ate point to come back here because -- it's hard to relive. Reporter: It was supposed to be a peaceful black lives matter protest in downtown Dallas. When it suddenly turned deadly. Over the next hours, the gunman terrorized the city. Singling out and shooting only white officers. The suspect has exchanged gunfire with us over the last 45 minutes, has told our negotiators that he's going to hurt and kill more of us. Reporter: Four officers were down, a fifth would die. The shooter had barricaded himself in a building. I'm going to have to get pack real quick. Reporter: Little did we know as we watched realtime the chief was about to implement a radical plan. Police chief deciding to send in a robot carrying a pound of plastic explosives. I'd do it again to save our officers' lives. There was some controversy after the fact how you took him out. An explosive to kill one guy? Yes, c-4. I was going to put those guys at more risk, I was going to have the guts to make a tough call. At best in a bad scenario your career could be over. Yes. I knew that. Nothing in me as a person or as a leader could have allowed someone else to take the risk that was clearly for me to take. Reporter: That buck stops here mentality but also his heartfelt candor on a national stage. We're asking cops to do too much in this country, we are. We're asking us to do too much. Every societal failure, we put it off on the cops to solve. Reporter: Won over the country. Become a part of the solution. Serve. Your community. Don't be a part of the problem. We're hiring. Get out there in the protest line and put an application in. Reporter: He says he's been a police chief in the making his entire life. The middle of three boys he learned about sacrifice, hard work, and giving back from the mother he adores. With the call to rise reinforced in his oakcliff church. How do you explain it? A kid from one of the toughest neighborhoods in Dallas, Texas, to go on to become the longest-serving police chief in modern history. The biggest tabkeaway is, I'm a product of a mother that just would never quit. Reporter: He excelled in high school. We took him back to reunite with his 12th grade teacher miss cox. This dynamic person here. This kid wants to learn everything. And you can't give him enough. I knew this was my shot. At getting out of poverty for my family. I knew it. Reporter: The straight "A" student went on to earn a full college scholarship. Then as chief brown, now an ABC news contributor, writes in his memoir "Call to rise," in the fall semester of his senior year his worlds collided. I was going to hang out with my buddies. One of the friends I knew, bumped into him, let's go play one on one babble. Basketball. Blank stare. Then up to another kid, same thing. Blank stare. Just daysed look. Zombies? Yes. Reporter: It was the beginning of the crack cocaine era. Whole neighborhoods were destroyed. Five or six rocks of crack cocaine. I had to do something. On a whim, went down to downtown Dallas and put an application in. Became a police officer. Reporter: He joined S.W.A.T. And quickly rose to squadron leader. You were a hammer up to that point? Hardcore. I was old-school police. I was proud of it. Po-lice. Police when you're being died, I was old-school po-lice. Kick in your door, put you in jail if youere doing drugs. Reporter: His success led to promotion and a surprise assignment in community police you hated it? The whole time. Reporter: He showed us the storefront where he was stationed. Hi, how are you? I'm okay, good to see you. Reporter: Then something happened. Changed the way I thought about policing. I just thought to myself, never got a chance to do it on a broader scale. Man, it would be something to see. Reporter: The opportunity came when he was named Dallas police chief. But then on father's day 2010, the unthinkable. His son D.J., who had undiagnosed adult onset bipolar disease, shot and killed two people, one a police officer. D.J. Himself was killed by a responding officer. You write, out of my tragedy two unexpected blessings emerged. When you find when you're at your wits' end in the most despair and distress you've ever experienced, it always points you toward serving others. Reporter: Tough moments that tested his faith. But adversity did not break him, it prepared him. And nearly one year after that massacre, the city he loves is still grateful. You changed my life, and I'm sure a host of other individuals' lives throughout the world. Because you gave us hope. You gave us hope. You're making my allergies act up, I've got to go. You gave us hope. Thank you. Thank you, miss cox. Reporter: I asked about those "Allergies" a little later. You got a little emotional? Very you -- you have your head down, grinding out a profession. Just trying to do it the right way. You never take the time to pay that much attention to the accolades. I just try to contain myself because I don't want to cry on TV. Yeah that's not -- that's not cool if you're a brother from oak cliff, that's just not what I want to try to do. Reporter: A brother from oak cliff. What's going on, bro? Reporter: A Texas taste of substance, style, who stayed home to serve. For "Nightline," I'm Byron Pitts in Dallas.
This transcript has been automatically generated and may not be 100% accurate.