A Mexican teenager who pleaded guilty to killing Border Patrol Agent Robert Rosas last year was sentenced Thursday to 40 years in prison. Christian Daniel Castro Alvarez, 17, was sentenced in federal court in downtown San Diego. About 100 Border Patrol agents in green uniforms filled the courtroom and lined the hallway outside to observe the court proceeding. Rosas, 30, was killed July 23 while on patrol near Shockey Truck Trail in Campo. About 9 p.m. that night, he was heard on his radio saying that he was tracking a group of illegal immigrants near the fence that marks the...