Air Force Staff Sgt. Luis Walker arrives for the fourth day of his trial at Lackland Air Force Base in San Antonio, Texas, Friday, July 20, 2012. Walker is accused of sexually assaulting 10 basic trainees, with charges ranging from rape and aggravated sexual assault to obstructing justice and violating rules of professional conduct. If convicted, he could be sentenced to life imprisonment.   (AP Photo/San Antonio Express News, Billy Calzada)