With Matt Gutman. Reporter: What would a hardcore gang member know about the intimacies of a teenage love triangle? In this case, prosecutors claim, quite a bit -- as they call to the stand a prisoner... See More
With Matt Gutman. Reporter: What would a hardcore gang member know about the intimacies of a teenage love triangle? In this case, prosecutors claim, quite a bit -- as they call to the stand a prisoner named Michael Angelo. With gun, drugs, and kidnapping chargdlmer??h'ame, he's a true renaissance man of crime. Are you a convicted felon? Yes, sir. Do you know how many times you've been convicted? Nine times. The plot thickened with Michael Angelo's testimony. Reporter: The felon shared a cell with Pedro bravo in the fall of 2012 and when they met, Angelo dispensed with the small talk. I was like, "You probably killed that kid," you know? What was his response to that? He really didn't answer. Reporter: Later, when bravo does speak, it's of his two main preoccupations -- writing and death. He had asked me, you know, to borrow a pen and my shoelace and I asked him, "What for?" And he said so that he could write a suicide letter to his parents and to use the shoestring to kill himself. Reporter: Bravo was put on suicide watch for a few weeks. Angelo says when the young man returns, bravo has shifted his mindset from suicidal to scheming. Now he's concocted a way to walk free. What did you think it was? A way to basically get the charges thrown out in his case or get the charges dropped against him. And did you believe it was offering you money to help? Yes, sir. Reporter: Bravo's plan was to use Angelo's outside gang contacts to commit murders similar to Chris' to make it appear that a serial killer was on the loose. Thus leading suspicion away from bravo. Was it ever brought up about the shovel and what you would need to do with the shovel as part of the plan? Reporter: The prosecutor keeps digging for more details, specifically about that shovel bravo purchased. I would have to go get the shovel to -- I guess, copycat that murder to make it look like somebody else had did it. Reporter: But Angelo had a plan of his own. He cut a deal with prosecutors to become a jailhouse snitch earning bravo's trust and extracting incriminating details like these. He was going to try to poison him with a mixture of sleeping pills and pesticide mixed with soda. His backup plan was to have a knife, you know, to cut his throat. And his main plan was to choke him with a moving strap. Reporter: Eventually Michael Angelo completes his masterpiece. A full confession from bravo. One the Aguilar family must now endure as the last moments of their son's life play out in graphic detail. He told me he basically put a moving strap around the kid's neck and braced himself against the seat. And he remembers watching the radio -- the clock on the radio -- and said it took like 13 minutes for the kid to, you know, I guess, die. Did he ever make any comment to about security guards at Walmart? Yeah. He -- at one point, he said that he kinda got freaked out because while he was holding onto the strap that -- the security guard had rode by. Reporter: Angelo is a full service snitch. He even leads cops to the hidden location of that now-infamous shovel. Did he tell you where he hid it? A wooden walkway. Reporter: Bravo's defense says Angelo's credibility is shot since he's testifying in exchange for a reduced sentence, but can they overcome all that video? Surveillance video at Walmart and at his apartment, you can see those two together. Reporter: With all that physical evidence piling up against him, the most important defense witness is Pedro bravo himself. In fact, the 20 year old is the only witness the defense calls. There were some reporters that even squealed. Two of them gasped. Everyone was waiting for that moment. Reporter: As his parents look on stoically, bravo tries to charm the jurors, resurrecting the old class clown, conversational, even jovial at times. Bravo describes his last ditch effort to win Erika back. I still loved her. And I really wanted to get back with her. I had this idea that, I'm going to go get her back. I'd keep telling myself, "You can do this, you can do this, you can do this." Reporter: But what exactly was the "This?" Bravo admits that when he discovered that Erika was dating Christian, he snapped. They've been going out for about, like, two or three weeks. And at that moment, I'm just instantly -- like, I'm crushed. Because he's one of my best friends. Reporter: He says that as he descended into a life of despair he was consumed by thoughts of suicide that had plagued him for years. I was too nervous to do anything -- I don't like pain -- and I couldn't bring myself to hang myself or anything like that. I tried to take some pills, see what would happen, but lo and behold, I'm still here. Reporter: Speaking of suicide, remember that shovel? Bravo can explain that away too. Tell the jury why you bought a shovel. It was gonna be part of my idea to kill myself. In a way, I was gonna go find a spot, and I was gonna mark my tomb and I was gonna dig it. Reporter: Even as the prosecution goes over his version of events, with dripping sarcasm, bravo remains cool. Now, you're on your way to kill yourself, right? Correct. But you gotta get gas first? Right? Correct. Okay. 'Cause you can't kill yourself without a tank of gas, correct? Correct. Reporter: And now, Pedro's biggest challenge is keeping all his stories straight. It seems like Pedro was changing his story to make it more believable depending on the evidence out there. Reporter: One piece of testimony that Pedro tries to finesse deals with the end of his encounter with Christian -- the alleged scuffle that began inside the SUV as the two boys argued over friman. His friend's nose now bloody, bravo claims he pulled in here behind this motorcycle shop. Now the two start fighting and tumble out of the car and at this point and claims things got really heated. As I exit the car, he comes up and something went from my head, and I just -- I got mad. I basically pushed him. As I pushed him, I followed behind him and I swept him off his feet. As he fell down, I fell on top of him as well. Reporter: Bravo claims that's the last time he ever saw Christian. Alive and above ground. But all I -- I could tell was that he didn't get up right away, but that he was still moving. Still breathing? Yes. Reporter: But here's the thing -- so much of this story was captured by security cameras. But the one piece of video Pedro needs to be on tape simply doesn't exist. We don't know of any video that shows the two had an encounter or a fight. Reporter: No video. And for 22 days, no Aguilar. Until his body is discovered face down in that shallow grave, buried, as cops say, "Enemy style." The defense tried to come up with a credible story. Now, do we believe that? I'm not sure. Reporter: But what does the jury believe? We're about to find out because as we were conducting this interview, a voice from the courthouse calls out. We got a verdict!
This transcript has been automatically generated and may not be 100% accurate.