Benton Police Chief Gary Sipes says it was an "unfortunate task" to have to arrest one of his own officers Tuesday on sexual assault charges. Assisted by the Saline County Prosecutor, the department completed its investigation into former Patrolman Frank Michael Calvin and fired him last Friday. Calvin is accused of using his position of authority to have sex with a woman who had been arrested and was being held at the police station. The arrest report says Calvin admitted to having sex with the woman while on duty and while in uniform, but he pleaded not guilty at Tuesday`s hearing. The Prosecutor says Calvin cannot use the argument that the sexual intercourse was consensual because state law defines any sex by clergy or other professionals of authority as third-degree sexual assault.