(CNN) -- Just hours after fatally shooting 17-year-old Trayvon Martin, George Zimmerman told police investigators the shooting followed a life-and-death struggle in which the teen told him, "You're going to die tonight."
The audio of the February 26 interviews, made public late Wednesday, is part of discovery items released by Zimmerman's defense team. The recordings represent the first time Zimmerman is heard giving his account in his own words.
Also released were audio and video showing the techniques used by the police department in the investigation: interviews conducted in the days after the shooting, a video of a voice stress test administered to Zimmerman by police and his videotaped re-enactment of the incident for authorities.
Zimmerman, 28, is charged with second-degree murder in Martin's February 26 shooting death. Zimmerman has said he shot Martin in self-defense, but Martin's family and civil rights activists across the country said Zimmerman, who is white and Hispanic, racially profiled Martin and ignored a 911 dispatcher's advice not to follow him.
In an interview just after the shooting, Zimmerman told police that the struggle began when Martin "jumped out from the bushes" and punched him in the face, knocking him down.
"I started screaming for help. I couldn't see. I couldn't breathe," he said.
"He grabbed my head and started hitting it into the sidewalk," he said. "When he started doing that, I slid into the grass to try to get out from under him. ... I'm still yelling for help."
Martin, he said, put his hand over Zimmerman's mouth and nose and told him, "You're going to die tonight."
"When I slid, my jacket and my shirt came up. ... I felt his hand go down my side, and I thought he was going for my firearm, so I grabbed it immediately, and as he banged my head again, I just pulled out my firearm and shot him."
When he did, he said, Martin, who had been on top of him, fell away and said, "All right. You got it. You got it." In another interview, he noted Martin might have said, "You got me."
Zimmerman said in the audio interviews that he was driving to the grocery store that evening when he saw Martin walking in his neighborhood. He said he pulled over and called a police nonemergency number "to report a suspicious person."
He noted that there had been some burglaries in the area, prompting him to start a neighborhood watch program. He said he had never seen Martin before and thought it odd that although it was raining, "he was just walking casually, not like he was trying to get out of the rain."
In another police interview on February 29, three days after the shooting, Zimmerman told Sanford, Florida, homicide investigator Chris Serino he also felt the youth was suspicious because he stopped in front of a home Zimmerman had previously called about, a home that was broken into after his reporting another suspicious person.
"Had this person been white, would you have felt the same way?" Serino asked. "Yes," Zimmerman replied.
As he spoke to the dispatcher, he told police Martin circled his vehicle, but he could not hear whether Martin said anything because his windows were up and he was on the phone. Afterward, he said, he "lost visual of (Martin)." At the same time, he said the dispatcher asked him his location. He said he wasn't sure of the name of the street he was on and got out of the vehicle to look for a street sign or an address on a home.
The dispatcher asked him if he was following Martin, he said, and he replied that he was "trying to find out where he went." The dispatcher told him, "We don't need you to do that," noting an officer was en route, he said.
Zimmerman said he was heading back to the vehicle when Martin jumped out, asking him, "What the f***'s your problem?"
He said he told Martin, "I don't have a problem," but the youth replied, "Now you have a problem," and attacked him. He said he fell backward after being punched in the nose, and "he was whaling on my head."
Zimmerman told police he yelled for help repeatedly and heard one man say he was going to call 911.
"I screamed 'Help me' probably 50 times, as loud as I could," he said.
In a written statement Zimmerman gave to police, also released late Wednesday, Zimmerman said Martin told him to "shut the f*** up" during the struggle.
"Each time I attempted to sit up, the suspect slammed my head into the sidewalk," he wrote. "My head felt like it was going to explode."
He wrote he felt Martin "reach for my now-exposed firearm" as the teen threatened his life and cursed at him.
During the videotaped voice stress test, he seemed to suggest that he wasn't sure he had hit Martin when he fired his gun, saying that he "thought that he heard the shot and he was giving up" and that he pushed Martin off of him.
"Either way, I ended up on top of him, straddling him," he said, but he claimed he "felt like (Martin) was hitting me with something in his hands" so he grabbed the youth's hands to restrain him. Martin was saying something like "ah, ah," and cursing, Zimmerman said, and he told him, "Stop. Don't move."
Before the voice stress test begins, Zimmerman discusses health insurance with a police officer and mentions he visited the doctor and the psychologist that day. "I think the psychologist is when it hit me the hardest," he said.
However, in a February 29 interview, Serino expresses some doubt about Zimmerman's account, noting that many questions remain about the incident.
"The court of public opinion is going to beat up on you a lot," Serino said. "A lot of people don't think that your injuries are consistent with getting into a life-threatening type thing."
Martin, Serino said, "has no criminal record whatsoever. Good kid. Mild-mannered kid."
In his possession, Serino said, "we found a can of iced tea and a bag of Skittles and about $40 in cash. Not a goon."
He tells Zimmerman he has received an anonymous phone call "from somebody who gave a different version of events ... more along the lines that you tried to detain him," and recounting an argument prior to the shooting.
"You got any problems with black people?" Serino asked Zimmerman, who replied, "No, sir."
Serino told Zimmerman authorities can't figure out what would have made Martin "snap." Zimmerman said he didn't know what might have enraged the teen.
And the investigator expresses doubt that Zimmerman, who had lived in the neighborhood for three years and described himself as head of the neighborhood watch, did not know the names of the three streets in the subdivision.
"To be honest with you, I have a bad memory anyway," Zimmerman said, adding that he has attention-deficit (hyperactivity) disorder and takes medication for it.
CNN's Vivian Kuo and Martin Savidge contributed to this report.