Because of this:how do you KNOW it was a gun? I just saw the word "weapon".
"Also, early Saturday morning, a source close to the investigation said deputies removed a weapon from the trunk of a car belonging to Casey' father, George Anthony. Such a discovery on the Anthony property could have imperiled Casey Anthony's release from jail, but a spokesman for Orange County Corrections said that a judge ruled that Casey presumably had nothing to do with the weapon."
(from the article cited). I doubt LE considers a tire iron, a lamp, a slim jim actual "court recognized' weapons. So, we must go with the simplest assumption: a gun. (someone tell me why one would keep a gun in the tire well? wouldn't you keep it under the seat, or, as a fashion statement, in a rack?