Police found a single shell casing at the scene, and when they seized George Zimmerman’s handgun, a Kel Tel 9 mm, its magazine was full, according to a source close to the investigation. The only bullet missing was the one in the chamber, the source said.
They found a casing at the scene. (a round was fired) They found a full magazine in the gun. (no live round was stripped from it and loaded in the chamber)
I get it the way I described it. I know people who routinely “top up” the magazine (usually by just putting a full one in) after they’ve chambered a round.