TEMPE, Ariz. (AP) -- A 22-year-old man pleaded not guilty on Wednesday in the beating death of his girlfriend, an Arizona State University student from Northfield, Minn. Luis Soltero is charged with murder, kidnapping and sexual assault in the killing of 19-year-old Rebecca Kasper, whose body was found in Soltero's Tempe apartment. Tempe police have said Soltero went to a police station to report Kasper's death and gave officers her Minnesota driver's license. Officers went to the apartment and found Kasper's body in the bathtub and covered with blankets and a rubber mat with a plastic bag over her head. Police said Kasper had blunt force trauma to the head and face. A dumbbell with blood on it was found near the bathtub.