A former Napa County school staffer is denying allegations of sexually abusing five children. Benjamin Casas, who worked at Pope Valley Elementary School, testified in his own defense on Tuesday. Casas is charged with 23 counts related to the alleged sexual abuse of five children, which prosecutors say began in January of 2013. The alleged victims, now adults, testified against Casas earlier in his trial. Casas also told the court he does not know how child pornography ended up on his computer.