A Los Angeles County sheriff's deputy has agreed to plead guilty to illegally building an assault rifle, marking the first plea agreement by one of 20 sheriff's officials charged or indicted since December in an ongoing federal investigation of the Sheriff's Department, authorities said Monday. Richard White Piquette admitted in a document filed in federal court last week that he manufactured a Noveske Rifleworks N-4 .223-caliber rifle with an eight-inch barrel. Under federal law, the rifle's barrel length should have been at least 16 inches, said Thom Mrozek, a spokesman for the U.S. attorney's office in Los Angeles. The charge...