Los Angeles police chief Charlie Beck holds an AR-15 assault rifle that was turned in as L.A. mayor Antonio Villaraigosa (L) looks on during a news conference at a gun buyback held by the Los Angeles Police Department in Los Angeles, California, Dec 26, 2012 following the mass shooting at Sandy Hook Elementary School in Connecticut. [Photo/Agencies]

A police officer lays numerous guns on the ground as their owner turns them in at a gun buyback held by the Los Angeles Police Department in Los Angeles, California, Dec 26, 2012 following the mass shooting at Sandy Hook Elementary School in Connecticut. [Photo/Agencies]