A former Boulder County deputy who resigned during an investigation last December has been obsessed with young girls for years, an arrest warrant affidavit states.The deputy, Rick Ferguson, 53, is accused of Internet exploitation of children. His interest in young girls "escalated and intensified" after he investigated a homicide in the late 1980s in which he "located and recovered dismembered remains" of a victim he knew, according to the affidavit unsealed on Thursday and obtained by the Longmont Times-Call.Ferguson was arrested in December after a county information technology employee reported on Nov. 17 that sexually explicit chats were found on a computer Ferguson used in his marked patrol car. The 30-year sheriff's department employee resigned after he was placed on leave during the investigation.Ferguson admitted to investigators that he used the online chat nickname "nitestick560" when he chatted with girls and women, according to the affidavit. Ferguson's badge number was 560, according to court records. The affidavit notes that chat records found his work and home computers were with several girls between the ages of 10 and 14. The chats were "primarily sexual in nature," according to the affidavit.Investigators said they do not believe Ferguson ever met the girls he chatted with. He lives in Broomfield.