A killer dentist would inject his lover with drugs to knock her out while they had sex, a double murder trial heard yesterday. Colin Howell and Hazel Stewart were both cheating on their spouses and the mother of two wanted to be unconscious so she would not experience any Christian guilt, the court was told.... Stewart, 47, denies murdering her husband Trevor Buchanan, 32, and Howell’s 31-year-old wife Lesley, whose bodies were found in a fume-filled car in 1991.... Asked by Neil Connor, prosecuting, why Howell gave her the sedatives, [a witness] replied: "So he could enjoy sexual gratification with her without her feeling guilt." Under cross examination, he indicated the guilt Stewart claimed to have experienced was in relation to her Christianity.