Attorneys representing George Zimmerman present their closing arguments on Friday, as jurors begin deliberating.

[WATCH/CHAT LIVE:  Tony Pipitone in courtroom | SPECIAL SECTION:  Zimmerman trial]

Zimmerman, 29, is charged with second-degree murder in the death of Trayvon Martin, who was shot and killed in a Sanford gated community in February 2012. 

Attorney Mark O'Mara began his closing arguments by casually thanking the jury before bringing up Zimmerman and put his hand on Zimmerman's shoulder as he discussed the presumption of innocence. He made references about Zimmerman moving to Florida and how he's married.

O'Mara told the jury "you don't know how to apply a standard reasonable doubt, you just don't." O'Mara said lawyers know how to apply reasonable doubt because they're used to it, but that he worries the jury will default back to their first impression of Zimmerman.

O'Mara then put on sunglasses and a pinkie ring to demonstrate how first impressions can influence your opinion and cloud your judgment.

"I think you have to be absolutely vigilant," O'Mara said to the jury.

Nine minutes into O'Mara's closing arguments, Martin's family walked in.

O'Mara told jurors they are not allowed to make a verdict based on assumptions.

"A just verdict is one without assumptions," O'Mara said, adding that Zimmerman is "not guilty of anything but protecting his own life."

O'Mara then attacked the prosecution's lack of definitive testimony.

"How many 'could-have-beens' and 'what-ifs' did you hear from prosecutors?" They should say 'without question,' certainty," O'Mara said.

O'Mara then brought out a poster explaining burden of proof to the jurors with the continuum of doubt: highly unlikely, less than likely, probably not, unlikely, may not be, perhaps, suspected, possibly guilty, etc.

"George Zimmerman is not guilty if you have reasonable doubt he acted in self-defense," O'Mara said.

He then discussed the state calling Zimmerman a "wannabe cop." O'Mara said Zimmerman did want to be a cop, as well as a prosecutor, lawyer and a helper.

O'Mara told jurors the state withheld a sixth non-emergency call Zimmerman made that didn't support the state's theory.

"The state wants you to hear 'I hate these young black males' in Zimmerman's calls," O'Mara said, mocking the suggestion that Zimmerman was frustrated on the non-emergency calls.

O'Mara then brought out a 10-foot-long timeline of Zimmerman call, showing "he's running" coinciding with when Martin's call with Rachel Jeantel disconnects the first time.

"The person who decided this was going to continue, that it was going to become a violent event was the guy who didn't go home when he had the chance to," O'Mara said.

O'Mara said the dispatcher told Zimmerman, "let me know if he (Martin) does anything else."

O'Mara then played the computer-animated reenactment that Judge Debra S. Nelson ruled couldn't be used in the trial as evidence, but could be used as demonstrative in closing arguments. O'Mara showed jurors where the defense "contend" Zimmerman was punched in the nose.

With the animation, the jury visualized a scene they have only seen in photos. The animation was also lined up with 911 calls. The jury will not be able to take back the animation to deliberate. 

O'Mara then started a stopwatch and let jurors sit in silence to demonstrate four minutes between Martin starting to run and the first 911 call.

"That four minutes is how long Trayvon Martin had to run (back home)," O'Mara said, calling it a "football throw length away." O'Mara suggested Martin ran, plotted and four minutes later, executed his attack on Zimmerman.

O'Mara then discussed Zimmerman's statement to his neighbor, Jonathon Manalo, who he told to call his wife. "Tell her I shot someone," O'Mara said Zimmerman told Manalo, not thinking of how insensitive it might sound a year-and-a-half later.