The Colorado attorney general's office has been appointed special prosecutor in the case of a former sheriff accused of trading methamphetamine for sex.Gov. John Hickenlooper announced the move Thursday in the case of 68-year-old Patrick Sullivan Jr., a former Arapahoe County sheriff. The Arapahoe County district attorney, Carol Chambers, asked to withdraw from the case.Sullivan faces charges of possession of methamphetamine, distribution of methamphetamine, attempting to influence a public servant and solicitation of a prostitute. He was arrested in November. Until he was released on bond on Dec. 6, he was being held in a jail that was named for him. Sullivan was sheriff from 1984 until 2002. A spokesman for the attorney general's office said Deputy Attorney General Michael Dougherty will be the lead prosecutor.