RIVERSIDE (CNS) - One of two men accused of fatally shooting a 33-year-old motorist during a car-to-car attack that began on a Riverside street and continued into the parking lot of a high school campus made his initial court appearance today. Arthur Joseph Henderson, 27, of Las Vegas was arrested Wednesday following a Riverside Police Department Robbery-Homicide Unit investigation into the slaying last month of Robert Moore of San Bernardino. Henderson is charged with first-degree murder, attempted murder and being a convicted felon in possession of a firearm, as well as sentence-enhancing gun and great bodily injury allegations. He appeared before Riverside County Superior Court Judge Gail O'Rane, who appointed him a public defender and scheduled his arraignment for Aug. 31 at the Riverside Hall of Justice. According to Riverside police Detective Steve Espinosa, the alleged attack on Moore happened in the predawn hours of July 5, beginning in the 3300 block of Central Avenue.