Update: Jury acquits George Zimmerman of 2nd-degree murder in Trayvon Martin shooting (poll)

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Neighborhood watch captain George Zimmerman was cleared of all charges Saturday in the shooting of Trayvon Martin, the unarmed black teenager whose killing unleashed furious debate across the U.S. over racial profiling, self-defense and equal justice.

Zimmerman, 29, blinked and barely smiled when the verdict was announced. He could have been convicted of second-degree murder or manslaughter. But the jury of six women, all but one of them white, reached a verdict of not guilty after deliberating well into the night Saturday. The jurors considered nearly three weeks of often wildly conflicting testimony over who was the aggressor on the rainy night the 17-year-old was shot while walking through the gated townhouse community where he was staying.

Defense attorneys said the case was classic self-defense, claiming Martin knocked Zimmerman down and was slamming the older man's head against the concrete sidewalk when Zimmerman fired his gun.

RELATED: Jury in Zimmerman trial enters second day of deliberation

"We're ecstatic with the results," defense attorney Mark O'Mara after the verdict. "George Zimmerman was never guilty of anything except protecting himself in self-defense."

Another member of his defense team, Don West, said: "I'm glad this jury kept this tragedy from becoming a travesty."

Prosecutors called Zimmerman a liar and portrayed him was a "wannabe cop" vigilante who had grown frustrated by break-ins in his neighborhood committed primarily by young black men. Zimmerman assumed Martin was up to no good and took the law into his own hands, prosecutors said.

State Attorney Angela Corey said after the verdict that she believed second-degree murder was the appropriate charge because Zimmerman's mindset "fit the bill of second-degree murder."

"We charged what we believed we could prove," Corey said.

As the verdict drew near, police and city leaders in the Orlando suburb of Sanford and other parts of Florida said they were taking precautions against the possibility of mass protests or unrest in the event of an acquittal.

"There is no party in this case who wants to see any violence," Seminole County Sheriff Don Eslinger said immediately after jurors began deliberating. "We have an expectation upon this announcement that our community will continue to act peacefully."

The verdict came a year and a half after civil rights protesters angrily demanded Zimmerman be prosecuted.

For his part, Tracy Martin — Trayvon Martin's father — posted his reaction to the verdict on Twitter:

Not arrested for 44 days

Zimmerman wasn't arrested for 44 days after the Feb. 26, 2012, shooting as police in Sanford insisted that Florida's Stand Your Ground law on self-defense prohibited them from bringing charges. Florida gives people wide latitude to use deadly force if they fear death or bodily harm.

Martin's parents, along with civil rights leaders such as the Revs. Jesse Jackson and Al Sharpton, argued that Zimmerman — whose father is white and whose mother is Hispanic — had racially profiled their son. And they accused investigators of dragging their feet because Martin was a black teenager.

Before a special prosecutor assigned to the case ordered Zimmerman's arrest, thousands of protesters gathered in Sanford, Miami, New York and elsewhere, many wearing hoodies like the one Martin had on the night he died. They also carried Skittles and a can of iced tea, items Martin had in his pocket. President Barack Obama weighed in, saying that if he had a son, "he'd look like Trayvon."

Despite the racially charged nature of the case, race was barely mentioned at the trial. Even after the verdict, prosecutors said race was not about race.

"This case has never been about race or the right to bear arms," Corey said. "We believe this case all along was about boundaries, and George Zimmerman exceeded those boundaries."

One exception was the testimony of Rachel Jeantel, the Miami teen who was talking to Martin by phone moments before he was shot. She said he described being followed by a "creepy-ass cracker" as he walked through the neighborhood.

Jeantel gave some of the trial's most riveting testimony. She said she overheard Martin demand, "What are you following me for?" and then yell, "Get off! Get off!" before his cellphone went dead.

The jurors had to sort out clashing testimony from 56 witnesses in all, including police, neighbors, friends and family members.

Differing accounts

For example, witnesses who got fleeting glimpses of the fight in the darkness gave differing accounts of who was on top. And Martin's parents and Zimmerman's parents both claimed that the person heard screaming for help in the background of a neighbor's 911 call was their son. Numerous other relatives and friends weighed in, too, as the recording was played over and over in court. Zimmerman had cuts and scrapes on his face and the back of his head, but prosecutors suggested the injuries were not serious.

To secure a second-degree murder conviction, prosecutors had to convince the jury that Zimmerman acted with a "depraved" state of mind — that is, with ill will, hatred or spite. Prosecutors said he demonstrated that when he muttered, "F------ punks. These a-------. They always get away" during a call to police as he watched Martin walk through his neighborhood.

To win a manslaughter conviction, prosecutors had to convince the jury only that Zimmerman killed without lawful justification.

Meanwhile, reaction began pouring in on social media to the verdict, including this tweet from the NAACP:

In Los Angeles, NBC-LA reporter Tena Ezzeddine posted an image of a gathering of protesters:

And in San Francisco, video journalist Sergio Quintana posted his own image of protesters there: