(CNN) – Jurors got to hear George Zimmerman's story in his own words for the first time Monday as his interviews with police were played in court.
The former neighborhood watch captain is charged with second-degree murder for killing 17-year-old Trayvon Martin in Sanford, Florida, on February 26, 2012. Zimmerman told police he was pursuing the teenager because there had been a rash of crime in the area. A confrontation ensued, and Zimmerman said he was forced to kill Martin.
"I tried to defend myself," Zimmerman said during his first police interview the night of the shooting. "He just started punching me in the face, and I started screaming for help. I couldn't see. I couldn't breathe."
Tape of Zimmerman's retelling of the confrontation between him and Martin could bolster the defense's key contention: that Zimmerman reacted in self-defense.
Zimmerman began his interview with investigator Doris Singleton by saying that there had been a lot of crime in the area and that he had started a neighborhood watch program. He said he spotted Martin, whom he thought looked suspicious, and began to follow him.
At some point, Martin circled Zimmerman's car as he followed him through the neighborhood, Zimmerman said, then the teenager disappeared into the "darkness."
"The dispatcher told me 'Where are you?' and I said 'I am trying to find out where he went,' and he said, 'We don't need you to do that,' and I said 'OK,'" Zimmerman told the investigator.
Zimmerman then started to head back to his car, he said, but never got there.
"(Martin) jumped out from the bushes, and he said, 'What the (expletive) is your problem, homie?' And I got my cell phone out to call 911 this time, and I said, 'I don't have a problem.' And he goes, 'Now you have a problem,' and he punched me in the nose," Zimmerman told the investigator.
Zimmerman said the blow knocked him to the ground, and Martin got on top of him.
"He puts his hand on my nose and my mouth, and he says 'You are going to die tonight,'" said Zimmerman. "As he banged my head again, I just pulled out my firearm and shot him... He is mounted on top of me, and I just shot him, and he falls off. And he's, like, 'Alright you got it, you got it.'"
Zimmerman met with police the day after the shooting to walk them through what he says happened the night he shot Martin. This interview was videotaped and played for jurors on Monday.
The lead investigator on the case, Chris Serino, met with Zimmerman briefly the night of the shooting and again three days later. He was the same officer who responded to the Martin family's missing person report, and he had some tough questions for Zimmerman to answer. He wanted to know why Zimmerman never identified himself as a neighborhood watch captain.
"Was it fear, precaution, safety or all of the above?" asked Serino.
"I didn't want to confront him," said Zimmerman.
Zimmerman insisted several times during this second interview that he didn't follow Martin and that he only exited his vehicle to find a street sign so he could give the location to police. Serino wanted to know why, after three years of living there, Zimmerman didn't know the names of the streets in his neighborhood.
"To be honest with you, I have a bad memory anyway," said Zimmerman.
Serino also wanted Zimmerman to tell him why he felt Martin looked suspicious.
"He was looking at the house intently, the same house I had called about before. He stopped in front of the house," said Zimmerman. "You know what, he's not walking briskly to get out of the rain. He didn't look like a marathon runner who trains in the rain. He was just walking slowly, and I said something's off. So that's why I called non-emergency."
Serino went on to play that call that Zimmerman made to police, stopping it along the way to press Zimmerman on certain statements he made, such as when he said the suspect looked like he was on drugs.
"On drugs, why?" asked Serino.
"He kept looking around. Looking behind him, just kept shifting where he was looking," said Zimmerman.
'"Something's wrong with him' – what's that statement?" asks Serino.
"I don't know," said Zimmerman.
At another point in the call, Zimmerman insisted to Serino that he wasn't following Martin, saying, "I was just going in the same direction as he was."
"That's following," Serino responded.
Serino also pointed out a specific point in the call where he says it would have taken Zimmerman a minute and 20 seconds to return to his car.
"You're in the rain getting wet ... you see where the obstacle is here? I want you to think about that. I'm speaking for you ... it doesn't sound like you quite recall exactly what happened at that point," said Serino. "It sounds like you're looking for him ... you want to catch the bad guy. (Expletive) punk can't get away... Did you pursue this kid? Did you want to catch him?"
"No," said Zimmerman.
The investigator then played a 911 call made by one of Zimmerman's neighbors, which captures screaming in the background and the gunshot that killed Martin.
"You hear that voice in the background? That's you. You hear yourself?" asked Serino.
"That doesn't even sound like me," said Zimmerman.
"I can't pinpoint where you were smothered, that's the problem I'm having," said Serino. "We don't hear (Martin) at all either. Is he being quiet? Is he whispering to you or something? Is he calm?"
"He's on top of me and he's telling me to, 'Shut the (expletive) up, shut the (expletive) up,'" said Zimmerman.
When defense attorney Mark O'Mara cross-examined Serino, he tried to downplay some of Serino's aggressive questioning, referring to it as a "challenge interview" and calling it a police technique.
"It's either going to tell you that you got him ... or it may confirm that he's, for the most part, telling you the truth," said O'Mara.
"Yes sir," said Serino.
"In this case, you didn't have much to hit him with?" asked O'Mara.
"No, sir, I did not," said Serino.
At one point during his interview with Zimmerman, Serino bluffed that he may have video of the incident shot on Martin's cellphone.
"I believe (Zimmerman's) words were, 'Thank God, I was hoping somebody would videotape it,'" said Serino. "Either he was telling the truth or he was a complete pathological liar. One of the two."
Serino says nothing indicated to him that Zimmerman was a liar.
"You think he was telling the truth?" asked O'Mara.
"Yes," said Serino.
Earlier Monday, in a surprise move, prosecutors called FBI senior scientist Hirotaka Nakasone to the stand to testify on whether it was possible to conduct voice analysis of the screams on a 911 call from the night of the shooting.
Nakasone has already testified as a defense witness in an evidentiary hearing about the admissibility of voice analysis technology and was slated to be called by the defense during its case.
Nakasone said the science of voice recognition cannot reliably identify the screams on the call, but he did say that someone who knows whoever was screaming on the call may be the best person to identify the voice. Prosecutors may have called Nakasone to help support the testimony of Martin's parents, who may testify that they recognize the screams as coming from their son.
Referring to the limitations of the technology, defense attorney Don West asked, "Science really doesn't help us in this case figure out who is screaming?"
"Unfortunately, that is correct," said Nakasone.
Testimony is scheduled to resume at 8 a.m. CT Tuesday, when lead investigator Serino is expected to continue answering questions from the defense.