Tonight, the fate of neighborhood watchman george zimmerman is now in the hands of that jury. Six women, the all-female jury, not given the case and sequesters until they decide his guilty or... See More
Tonight, the fate of neighborhood watchman george zimmerman is now in the hands of that jury. Six women, the all-female jury, not given the case and sequesters until they decide his guilty or innocence. If connected, second degree murder in the killing of trayvon martin, george zimmerman could spend the rest of his life behind bars. And that jury will be deciding his fate based on just a single word. The word "help" and who was screaming it in the background of a chaotic 911 call. Here's matt gutman, who has been on the case in florida since the story first broke. Your verdict, finding george zimmerman either not guilty or guilty must be unanimous. Reporter: The jury has the case after a tense three week trial filled with courtroom fireworks. He automatically assumed trayvon martin was criminal. Reporter: The impossibly long hours and short tempers, even had the judge storming out on the legal teams. Finally, there will be an answer to the burning question, did george zimmerman kill trayvon martin? Was it murder, manslaughter or self-defense? The tale of how martin and zimmerman's paths fatally collided started here in sanford, florida, a small bedroom community on the fringe of "the world's happiest city," orlando. But it's a long way from the theme park crowds on a raw february night inside this gated sanford community. This guy looks like he' to no good, or he's on drugs or something. Reporter: That's the voice of george zimmerman -- and the "guy" he's talking about is trayvon martin, earlier seen buying an arizona drink and skittles at a 7-eleven. Martin was heading back to his father's fiance's home in the housing complex where he was spending a ten-day school suspension after getting busted on a pot-related offense. Something the jurors never heard. Despite his youthful indiscretions, his family says martin was just a normal teenage kid into girls, rap music and airplanes. E was interested in flying planes. That fascinated him, which led him to go to a program to, you know, try to pursue his career in aviation. Reporter: Is there one thing that you miss most about him? I miss his smile. He was a very affectionate teenager, so, I just miss him smiling and giving me a hug. It's raining and he's just walking around, looking about. Reporter: Initially, martin didn't know he was being tailed by zimmerman, the self-appointed neighborhood watch captain. By day, an auditor. By night, zimmerman, who had a past interest in law enforcement, kept a wary eye out on behalf of his neighbors. Reporter: What was your first impression of this guy? I thought he was meek and easy going, and at first, I had a little trepidation that guy guy was going to run the neighborhood watch. Reporter: How do you think he did as a neighborhood watchman? Fantastic. You know, his efforts and diligence yielded results. And that firearm -- Reporter: But in court, prosecutors painted zimmerman as an over-zealous wannabe cop. His language in this non-emergency call to police sparked the racial debate over the case. She's got his hand in his waistband. And he's a black male. Reporter: Fueled allegations that he was aggressively profiling a harmless teenage student. Just let me know if this guy does anything else. Okay. These , they always get away. punks. Theep ], they always get away. Those were the words in that grown man's mouth as he followed in the dark a 17-year-old boy. The prosecution wants to make it clear that he already had a mindset when he got out of his car and began to follow trayvon martin. Armed with a fully loaded semiautomatic piston. Reporter: Prosecutors argue that zimmerman was hell bent on stalking martin, even when told by police to call it off. Are you following him? Yeah. Okay, we don't need you to do that. Okay. Reporter: And then zimmerman hangs up. At that point, martin is in the last phone call of his life, with his friend, rachel jeantel and she says he's racked with worry about the mysterious man shadowing him. He just told me the man, the man looked creepy and -- he said the man looked creepy? Creepy, white. Okay. Excuse my language, cracker. Reporter: Jeantel says she told martin to run away, but then she says she heard him being confronted by zimmerman. "Why are you following me for?" And then I heard a hard breath man come say, "what are you doing around here?" And then I started to hear a little bit of trayvon saying, "get off, get off." Reporter: This is the path where the lives of martin and zimmerman collided that night. And out here for 30, 40 seconds, there is a black hole of information, until dispatchers from 911 started getting flooded with calls. They're wrestling right in the back of my porch. Someone's yelling, two doors down from me, screaming, hollering, help, help, help. Reporter: Then, a gunshot shatters the night. Oh my god, somebody could be shot. Oh my god. And there's a black guy down and it looks like he's been shot and he's dead. George zimmerman did not shoot trayvon martin because he had to. He shot him for the worst of all reasons, because he wanted to. He said, "yo, you got a problem?" Reporter: But in this police reenactment, zimmerman says it was he who was confronted by an angry trayvon martin. He said, "you got a problem now?" And then he was here and he punched me on the face. He got on top of me somewhere around here, and that's when i started screaming for help, i started screaming "help" as loud as I could. I tried to it is up and that's when he grabbed me by the head and tried to slam my head down. Reporter: Zimmerman says the confrontation escalated after martin spotted the gun on his hip. He looked at it, and he said, "you're going to die tonight, ." And he reached for it, I felt his arm going down to my side and I grabbed it and I just grabbed my firearm and I shot him. One time. After you shot him, what did he say? After I shot him, he like sat up and said "oh, you got me." Reporter: About two minutes after the shot rang out, this photo was taken at the scene. The defense says it confirmed zimmerman's account that he was attacked by martin. And in court, even a neighbor called as a prosecution witness appeared to back up zimmerman's account that he was the one being attacked. I could tell the person on the bottom had a lighter skin color. Reporter: The jury has been presented with two completely contradictory accounts of what happened with no solid evidence to back up either side's claims. That is, until a critical piece of evidence is introduced. I'm going to play the whole thing. Reporter: A 911 call where a voice is heard screaming for help. Help! There's someone screaming outside. Help! Do you think he's yelling help? Yes. ReporteREAMS IN 40 seconds. The critical question, does that desperate voice belong to trayvon martin or george zimmerman? If the jurors believe that it was george zimmerman screaming out for help, then it supports his theory that he acted in self-defense. I thought it was george. Reporter: To identify the voice, the defense calls a parade of zimmerman's friends -- who perhaps, not surprisingly, say it's him on the tape. Do you know whose voice that is in the background screaming? Yes, definitely. It's georgie, I hear it. I hear him screaming. There's absolutely no doubt in my mind that is george zimmerman. Reporter: The mothers of both martin and zimmerman also take the stand and they confidently identify the voice as that of their son. Who do you recognize that to be, ma'am? Trayvon benjamin martin. I'm sure that's george's voice. Defense calls tracy martin, your honor. Reporter: But then the defense calls a more unlikely witness. So help you god? I. Reporter: Trayvon martin's father, tracy martin. Police said martin informed them after the shooting that he did not believe the voice on the tape was his son's. But on the stand, martin seems to change his story, saying that after hearing the tape over 20 times, he's now convinced it was his son crying for help. I was listening to my son's last cry for help. I was listening to his life being taken. And I was coming to grips that trayvon was here no more. I think at the end of the day, the testimony of these witnesses will cancel themselves out. The jurors are going to have to listen to that 911 tape and they're going to have to decide for themselves who they believe that voice is. Reporter: And the only person who knows exactly what happened that night? The defendant, george zimmerman. Reporter: Decided not to testify in his own defense. After consulting with counsel, not to testify, your honor. Reporter: But the testimony of this woman, the so-called star witness, had everyone talking. A lot of people criticized her for her hair, for her skin, her darker skin tone. Reporter: And her answers raised an ugly taboo. Race. We can't get justice for a young black boy. To say this case is not about
This transcript has been automatically generated and may not be 100% accurate.