Transcript for Trayvon Martin's parents describe taking on new roles as activists

The parents turning anguish into action. The death of their son trayvon martin sparked protests around the country and now, five years later, they're revealing how their pain has pushed them to become champions against gun violence. Here's my "Nightline" coanchor Byron Pitts. No justice, no peace! No justice, no peace! Reporter: It's 9:00 A.M. On the sunny streets of Miami gardens, Florida. And an American rainbow, young and old, black and white, here to commemorate the life and death of trayvon martin. It was five years ago this month when 17-year-old trayvon martin, unarmed, holding a bag of skittles and the a bottle of iced tea, was shot and killed by neighborhood watchman George Zimmerman. I still want justice for trayvon. Reporter: His parents leading the charge to stem the wave of gun violence. Across America an average of 309 people are shot every single day. What's it say to you all these years later, people still come out like this? It shows how engaged everybody is. That everybody still want to be a part of the movement. Reporter: Zimmerman's subsequent trial and acquittal transfixed the nation. Trayvon martin! Reporter: Spark the rallying cry we call black lives matter. There are many who say that trayvon martin became Emmett till for a new generation of activists in our country. I think trayvon certainly re-energized a civil rights movement in this country. This was a child who lost his life to a senseless act of violence, gun violence, to someone who wanted to be a vigilante. Reporter: Tracy martin and Sabrina Fulton penned a powerful memoir called "Rest in power: The enduring life of trayvon martin," a retrospective look back at the son they raised and a tragic event that would change their lives. Mom, your boy would be 22 years old this month. How are you doing? Fairly well. I still have my good days and bad days. I still think about him and cry. I also think about him and smile too. You're smiling now. Yeah. Because I'm thinking about him. If he was still with us, that he would be graduating from college this year. He was very outgoing. Outdoorsman, I used to call him. He loved doing things outdoors. So just to have his life cut short and taken away from him and not to see him continue to do the things that he likes, it was very devastating. Reporter: That bullet from George Zimmerman's gun pierced trayvon martin's heart and exposed an old wound in America's soul. We want arrests! Reporter: With no arrests for six weeks, Florida's controversial stand your ground law came into sharp focus. Stand your ground lives enormous leeway to people like Zimmerman to use deadly force if they feel threatened. Reporter: It divided our nation with many Americans asking, what if Zimmerman had been black? If a black man had come into a white neighborhood and gunned down a 17-year-old boy, all hell would let loose. Reporter: And soon celebrities and everyday citizens made more than a fashion statement. They took a stand. The clenched fist of the 1960s was a hoodie like one worn by trayvon the night he died. Culminating in the hoodie March in New York City. The message made its way to the white house. When I think about this boy, I think about my own kids. If I had a son, he'd look like trayvon. Trayvon was dead on the ground at 17, unarmed. And he was given a drug and alcohol test and a background check, but the person who was shot and killed him, who was still holding the gun, he went home. My son went to the medical examiner's. And this person went and got in his bed as if nothing happened. Reporter: Fulton and martin have painted a picture of the confusion and frustration that immediately followed. There was something else in the book I was struck by this notion that there's this 17-year-old boy dead on the sidewalk. Police don't canvass the neighborhood, they don't knock on doors to say, is this your son? Why not? I couldn't tell you that. When I returned to the residence that night, the crime scene tape had been taken down and there was no sign of any altercations on the scene. And so it still isn't clear to me. So trayvon was listed as what, initially? When they took his body in? John doe. We had to fight to get trayvon's body back so that we can ship -- have the body shipped home. We didn't ask for anything that any other parents wouldn't have asked for for a 17-year-old. Reporter: Once the Zimmerman trial was under way a year later, martin's parents would face another difficult challenge, facing the man who killed their boy. Trayvon was no comparison to somebody that was 28 years old with a loaded gun. He was 17 years old, unarmed, and on the telephone at the time. Not guilty in the George Zimmerman trial -- Reporter: Zimmerman would walk out of that courtroom a Freeman. Of course we're shocked and disappointed. Reporter: That not guilty verdict would mark the beginning of Tracy and Sabrina's new life as activists. Trayvon martin was you! Reporter: They founded the trayvon martin foundation at Florida memorial university. Everything in here is trayvon. Reporter: Sabrina spoke at the democratic national convention last summer. I am here today for my son, trayvon martin, who is in heaven. Reporter: Campaigned heavily for Hillary Clinton. She's even thinking about running for office herself. How does one go from being reluctant to even have your name mentioned in public because you are a grieving mom, to now being someone who's considering running for office? I would not have imagined this but sometimes your life, you are dealt cards and the you need to make sure that you're playing the hand right. What do you expect from president trump? We don't know what his plans are for gun violence. We don't know what his plans are for the African-American community. Are you optimistic? Hard to say. It's hard to say. No justice, no peace! Reporter: At the remembrance March there's lingering sadness over another more recent shooting. Three teens were shot while walking home from Miami Carroll senior high -- Reporter: Hours later, in the same neighborhood, three teens shot on their way home from school in a drive-by shooting. Part what was seems to galvanize people in this movement, it was a white guy accused of killing a black teenager. What happened here last night most likely was black on black. We know that black on black crime is plaguing our community. It's something that we have to deal with as citizens. Just have to work at it piece by piece by piece. Reporter: A cruel irony depicting the ugly cycle of gun violence in this case, all three teens are expected to make full recoveries. I would imagine that knowing that your son is the face of a movement has to energize you in some way. But I would also mention, it can be a tremendous burden, yes? I would much rather prefer my life as it was. To have both boys here, to just be going on vacation and going to work every day, and them going to school. But I know that it's not just about trayvon martin, it's about so many other trayvon Martins. It's about our young ladies being shot and killed. It's about our teenagers being shot and killed. Men being shot and killed. So it's so much bigger than trayvon that we really didn't understand initially, but I think we kind of get it now, that it's very important that we continue this fight. Reporter: For "Nightline," I'm Byron Pitts in Miami. Next, we switch gears and

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