Lyon sisters-thumbWHEATON, Md. (AP) _ Prosecutors face several challenges as they attempt to prove that a man they’ve charged is responsible for the 40-year-old slaying of two sisters who were abducted from a mall. Among the obstacles: The suspect says he didn’t do it, no bodies have been found, and other physical evidence has vanished. Authorities announced on Wednesday that convicted sex offender Lloyd Lee Michael Welch Jr. has been charged in the deaths of the Lyon sisters, 12-year-old Sheila and 10-year-old Katharine. They vanished from a suburban shopping mall near their home in Wheaton, Maryland, in 1975. According to the indictments, the girls were slain in Bedford County, Virginia, about 200 miles away. Bedford County commonwealth’s attorney Randy Krantz says he and his colleagues face “a difficult burden.” Court documents show Welch told police he left the mall with the girls but denied killing them.