George Zimmerman George Zimmerman smiles as attorney Mark O’Mara questions potential jurors. (Gary Green, Orlando Sentinel via AP)

Opening arguments start today in the second-degree murder trial of George Zimmerman, almost one year and four months after he killed Trayvon Martin. An all-female jury will determine whether the neighborhood watch volunteer who shot the unarmed teenager acted in self-defense. Thanks to Florida’s incredible sunshine laws, the public knows much more about the case than will be revealed at trial. But it is what will be presented — and not presented — in that Florida courtroom over the next two to four weeks that will determine Zimmerman’s fate.

Seminole County Circuit Judge Debra Nelson has given the prosecution and the defense reason to feel cautiously optimistic about their chances with the jury. Nelson ruled last month that the defense is not allowed to mention Trayvon’s social media communications, his school suspension and drug use in their opening statement. Not that any of that information justifies Zimmerman’s actions that rainy evening on Feb. 26, 2012.

Last week, Nelson ruled the prosecution can say in its opening statement that Zimmerman was a “wannabe cop” and a “vigilante.” They can also say he “profiled” Trayvon. The phrase “racially profiled” is not allowed. But over the weekend, Nelson ruled the prosecution cannot call two audio experts who would testify that the person heard screaming on 911 calls was Trayvon. “There is no evidence to establish that their scientific techniques have been tested and found reliable,” Nelson wrote in her decision.

So we’re now looking at two pivotal moments in the trial. As Kendall Coffey, former U.S. attorney for the Southern District of Florida, told NBC News last night, the testimony of Witness 8 is now crucial for the prosecution. She is the one who was on the phone with Trayvon in his final moments. Because she is an earwitness, albeit a flawed one, to what happened, she is the closest we’ll come to knowing from Trayvon’s perspective what happened that night.

And for the defense, keeping Zimmerman off the stand is paramount. Telling his version of events would no doubt be helpful to his case. But cross-examination by the prosecution could be withering. From the precious little DNA evidence to back up his story to Trayvon’s hands, Zimmerman could be his own worst enemy in explaining how he killed a teenager armed with only a bag of Skittles and iced tea.

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