George Zimmerman "A Free Man"

CNN) -- George Zimmerman is not guilty of murder in the death of Trayvon Martin, a Florida jury decided late Saturday.

The fact that Zimmerman fired the bullet that killed Martin was never in question, but the verdict means the six-person jury had reasonable doubt that the shooting amounted to a criminal act.

The verdict caps a case that has inflamed passions for well over a year, much of it focused on race and gun rights.

The jury -- made up of all women -- had three choices: to find Zimmerman guilty of second-degree murder; to find him guilty of the lesser charge of manslaughter; or to find him not guilty.

The jurors deliberated for 16½ hours total, including 13 on Saturday alone, before delivering their verdict.

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When he learned his fate, a subdued Zimmerman had little visible reaction. His face was mostly expressionless. He turned and shook the hand of one of his attorneys before sitting back down, only openly smiling after the court was adjourned. His parents, Robert and Gladys Zimmerman, were seated nearby, but Martin's parents were not in the courtroom.

After the verdict, Trayvon Martin's father, Tracy Martin, tweeted "God blessed Me & Sybrina with Tray and even in his death I know my baby proud of the FIGHT we along with all of you put up for him GOD BLESS."

"Thanks to everyone who are with us and who will be with us... we together can make sure that this doesn't happen again," said another tweet from Trayvon's father.

Earlier in the day, the jury had asked the court for clarification on its instructions regarding manslaughter. The jury couldn't have even posed such a query a few days ago: Judge Debra Nelson ruled Thursday, over the defense's vehement objection, to include manslaughter as an option for jurors, in addition to a second-degree murder charge.

To convict Zimmerman of manslaughter, the jurors would have had to believe that he "intentionally committed an act or acts that caused the death of Trayvon Martin." That charge could have carried a sentence of up to 30 years in prison, though the jury was not told of that possible sentence.

For second-degree murder, the jurors would have had to believe that Martin's unlawful killing was "done from ill will, hatred, spite or an evil intent" and would be "of such a nature that the act itself indicates an indifference to human life."

Ultimately, they believed neither. And that means Zimmerman can walk free.

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Scores who had gathered outside the Sanford, Florida, courtroom hoping for a guilty verdict reacted in disbelief after word of the decision trickled through the crowd. Hours earlier, they had given speeches, singing songs and chanting, "We want justice." Some appeared angry, others appeared sad.

They weren't alone: All day, there were also Zimmerman supporters in the courtyard holding signs saying "Self-defense is a basic human right," "Not enough evidence," and plainly "Not guilty." They had an entirely different view of the case: that Zimmerman had been wrongly implicated, that he'd just done what he could to save his life.

Florida State Attorney Angela Corey defended the second-degree murder charge that was filed against Zimmerman, telling reporters late Saturday that the allegations "fit the bill" for the charge.

"We believe that we brought out the truth on behalf of Trayvon Martin," Corey told reporters shortly after the verdict was announced.

One of her prosecutors, Bernie de la Rionda, expressed disappointment with the jury's decision, but acceptance as well.

"It's not perfect, but it's the best of the world," he said of the jury system. "And we respect the jury's verdict."

The response from NAACP President Benjamin Todd Jealous struck a far different tone.

"We are outraged and heartbroken over today's verdict," Jealous said in a statement, vowing to pursue "civil rights charges" in the case. "We stand with Trayvon's family, and we are called to act."

The fateful night

The story started the night of February 26, 2012, as Martin walked back to his father's fiancee's house through the rain from a Sanford convenience store, where he'd bought Skittles and a drink.

Zimmerman, a neighborhood watch volunteer, spotted him and called police. A 911 dispatcher told Zimmerman that officers were on the way and not to follow the allegedly suspicious person.

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Nonetheless, Zimmerman got out of his car, later telling police he just wanted to get a definitive address to relay to authorities.

Sometime after that, Zimmerman and Martin got into a physical altercation. Some neighbors took notice: On one 911 call, anguished cries for help can be heard.

Who was yelling? Martin's mother testified she's "absolutely" sure it was her son; Zimmerman's parents said, with as much conviction, that it was their own child.

There are also disputes about who was the aggressor, about whether or not Martin may have seen or reached for Zimmerman's gun, about whether Zimmerman should have had more injuries if he was pummeled, as he claims.

And some accused Zimmerman -- who identifies himself as Hispanic -- of racially profiling the black teenager, a claim the defense camp flatly denied.

About the only thing not in dispute is that the now 29-year-old Zimmerman shot and killed Martin.

Prosecution: 'He shot him because he wanted to'

In his closing argument, Assistant State Attorney Bernie de la Rionda noted that -- for all the evidence presented -- the case boils down to two men. One of them, Martin, is dead and can't give his side of the story. The other, according to the prosecutor, cannot be trusted.

De la Rionda asked: Why would a scared man get out of his car and walk around after being told not to? Shouldn't Zimmerman have had more than a bloody nose and scratches on his head given the beating he allegedly took? And did he have an agenda -- to do whatever necessary to stop one of those "f***ing punks," as he's heard saying under his breath in his call to police, from getting away?

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Assistant State Attorney John Guy made the prosecution's final pitch, during the rebuttal phase of closing arguments Friday. He echoed many points de la Rionda had made earlier, portraying Zimmerman as a frustrated wannabe police officer who took the law into his own hands. He had decided Martin was one of the criminals who had been victimizing his neighborhood, he said, then trailed him against the advice of police dispatchers.

"The defendant didn't shoot Trayvon Martin because he had to," Guy said. "He shot him because he wanted to. That's the bottom line."

Zimmerman, the prosecution said, had a powerful determination not to allow someone he had already decided was a criminal to escape.

"What is that when a grown man, frustrated, angry, with hate in his heart, gets out of his car with a loaded gun and follows a child? A stranger? In the dark? And shoots him through his heart? What is that?" Guy asked.

Defense: Zimmerman deserves benefit of the doubt

In the opinion of defense attorney Mark O'Mara, what George Zimmerman did was simple: he defended himself.

Zimmerman was looking out for those in his neighborhood when he saw someone he felt was suspicious and called police, O'Mara said in his closing argument. The defendant got out of his car, but briefly, and was walking back to it when things got physical.

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Martin jumped out of some bushes and pounced, the defense contends. And, O'Mara added, the teen didn't just hold Zimmerman down, but punched and slammed his head repeatedly into the sidewalk.

"That was somebody who used the availability of dangerous items, from his fist to the concrete, to cause great bodily injury against George Zimmerman," said O'Mara.

The lead defense attorney also criticized the prosecution's case, saying it was full of "coulda beens. How many 'what ifs' have you heard from the state in this case?" There's no merit, he claimed, to the depiction of Zimmerman as a frustrated, spiteful man seeking vengeance.

"Do not give anybody the benefit of the doubt except for George Zimmerman," O'Mara said.

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In the weeks after Martin's death, tens of thousands attended rallies led by civil rights activists demanding Zimmerman's arrest and chastising authorities for their handling of the case.

Zimmerman surmised Martin was a criminal like those who'd struck in his neighborhood before -- at least one of whom was black -- a lawyer for the late teen's family said Friday. But Martin was not a criminal, which Daryl Parks said contributes to the racial tensions that still surround this case.

While he wouldn't call Zimmerman a racist, "this case in its totality has a racial undertone to it," Parks told CNN's Anderson Cooper.

The defense strongly rejected accusations Zimmerman is racist, with O'Mara citing his client's work as a mentor to black children and his taking a black girl to his prom as evidence of his non-racist beliefs.

His defenders have been passionate as well, especially about a person's right to defend himself with a gun when attacked. Debate swirled over Florida's "stand your ground" law, which allows those who believe they are in imminent danger to use deadly force to protect themselves.

In light of this ongoing fervor, authorities asked for calm while setting up contingency plans to respond to incidents tied to a verdict. The Rev. Jesse Jackson Jr. was among those appealing for peace Friday, while Zimmerman's family urged people to "respect the rule of law, which begins with respecting the verdict."

"Freedom of expression is a constitutional right," said the sheriff's office in Broward County, in the Miami area. "While raising your voice is encouraged, using your hands is not."

But O'Mara said that, whatever the outcome, his client will not feel safe.

"There are a percentage of the population who are angry, they're upset, and they may well take it out on him," he said.