Before the defense began its case, defense attorney Mark O'Mara argued Zimmerman should be acquitted, saying prosecutors hadn't proved their case.
"What is before the court is an enormous amount of information my client acted in self-defense," O'Mara told Judge Debra Nelson, who continued to listen to arguments late Friday afternoon.
Before the state rested, Martin's mother, Sybrina Fulton, sat expressionless on the witness stand while prosecutors played the 911 recording, in which high-pitched wails can be heard as Zimmerman's neighbor urges a dispatcher to send police quickly. Moments later on the call, there is a gunshot and the crying stops.
"Who do you recognize that to be?" prosecutor Bernie de la Rionda asked Fulton.
"Trayvon Benjamin Martin," she replied.
She was followed on the stand by her son Jahvaris Fulton, Martin's 23-year-old half brother, who also testified the cries came from Martin.
Identifying the voice could be critical to the case because it could help the jury determine who was the aggressor during the scuffle that ended with Zimmerman killing Martin. Zimmerman's father has claimed it's his son yelling.
Zimmerman, the former neighborhood watch volunteer charged with second-degree murder, has said he shot the teen in self-defense during a fight.
Late in the afternoon, the prosecution rested after calling 38 witnesses over two weeks.
When introducing herself to jurors, Sybrina Fulton described having two sons, one of whom "is in heaven."
During cross-examination, O'Mara suggested - haltingly, in apparent recognition of the sensitivity of the questioning - that Fulton may have been influenced by others who listened to the 911 call, including relatives and her former husband.
O'Mara asked Fulton hypothetically whether she would have to accept that it was Zimmerman yelling for help if the screams did not come from her son.
"I heard my son screaming," Fulton answered firmly.
The defense attorney also asked Fulton whether she hoped Martin didn't do anything that led to his death.
"I would hope for this to never have happened and he would still be here," she said.
O'Mara asked Jahvaris Fulton why he told a reporter last year that he wasn't sure if the voice belonged to Martin. Jahvaris Fulton explained that he was "shocked" when he heard it.
"I didn't want to believe it was him," he said.
O'Mara asked to play the TV interview for jurors, but the judge denied his request for the time being.
Before testifying, Sybrina Fulton posted on Twitter: "I pray that God gives me the strength to properly represent my Angel Trayvon."
After the mother and brother testified, the doctor who performed an autopsy on Martin took the stand. Associate Medical Examiner Shiping Bao started describing Martin as being in pain and suffering after he was shot, but defense attorneys objected and the judge directed Bao away from that line of questioning.
He later estimated that Martin lived one to 10 minutes after he was shot, and said the bullet went from the front to the back of the teen's chest, piercing his heart.
"There was no chance he could survive," Bao said.
With jurors out of the courtroom, Bao acknowledged under defense questioning he had changed his opinion in recent weeks on two matters related to the teen's death - how long Martin was alive after being shot and the effect of marijuana detected in Martin's body at the time of his death.
Bao said last November that he believed Martin was alive one to three minutes. He also said Friday that marijuana could have affected Martin physically or mentally; he said the opposite last year.
The judge ruled before the trial that Martin's past marijuana use couldn't be introduced, and so the jury did not hear Bao's opinion about the drug's effect.
Zimmerman attorney Don West questioned why Martin's hands weren't covered to preserve evidence on his fingers and why it took three hours to remove the body from the scene. West and Bao talked over each other at several points, prompting the judge to tell everyone to speak one at a time.