SANFORD, Fla. — George Zimmerman’s lawyers put a concrete slab and two life-size cardboard cutouts in front of the jury box today in one last attempt to convince the panel the neighborhood watch volunteer shot Trayvon Martin, 17, in self-defense.

The jury in the murder case is expected to begin deliberations this afternoon after receiving dueling portraits of Zimmerman: a wannabe cop who took the law into his own hands, or a well-meaning volunteer who feared for his life in a struggle with a teenager who was slamming his head into the pavement.

Attorney Mark O’Mara used a concrete slab to make the point that it could be used as a weapon. He also used cardboard cutouts of Zimmerman and Martin to demonstrate that the teenager was considerably taller. He also showed a computer-animated depiction of the fight based on Zimmerman’s account.

He said that prosecutors hadn’t met their burden of proving Zimmerman’s guilt beyond a reasonable doubt. Instead, he said, the murder case was built on “could’ve beens” and “maybes.”

“If it hasn’t been proven, it’s just not there,” O’Mara said. “You can’t fill in the gaps. You can’t connect the dots. You’re not allowed to.”

In a rebuttal, prosecutor John Guy accused Zimmerman of telling “so many lies.” He said Martin’s last emotion was one of fear as Zimmerman followed him in a neighborhood of townhomes on a rainy night Feb. 26, 2012.

“Isn’t that every child’s worst nightmare, to be followed on the way home in the dark by a stranger?” Guy said. “Isn’t that every child’s worst fear?”

The jury of six women will have to sort through a lot conflicting testimony from police, neighbors, friends and family members. Witnesses gave differing accounts of who was on top during the struggle, and Martin’s parents and Zimmerman’s parents both claimed that the voice heard screaming for help in the background of a 911 call was their son’s.

Zimmerman, 29, is charged with second-degree murder, but the jury will also be allowed to consider manslaughter. Under Florida’s laws involving gun crimes, manslaughter could end up carrying a penalty as heavy as the one for second-degree murder: life in prison.