Three people are behind bars in Knox County facing drug charges after police arrested them in separate incidents earlier this month. One of them is accused of being a major cocaine dealer in the Rockland area. 45-year-old John Wall of South Thomaston is charged with selling cocaine and violating probation. Drug agents arrested him last week, hiding in a house in Monmonth. Police say he’s been eluding authorities since spring and was a supplier for several people who’ve already been charged with selling coke. 40-year-old David Libby of Rockland is accused of selling the prescription drug, Xanax.He was arrested two weeks ago. During the investigation, agents say they also discovered his fiance, 36-year-old Charlotte Shellman of Rockland, selling Xanax as well as the medication Ritalin.