A Mount Airy man has begun serving an 18-year sentence in the federal prison system for sexually molesting and videotaping twin sisters over a seven-year period.

Isaac Lee Smathers Jr., 62, formerly of 169 Slate Mountain Road, was tried in a recent session of U.S. District Court.

He had been arrested in September 2007 by detectives with the Surry County Sheriff’s Office on multiple sex crimes involving the girls, who were then 13 years old.

The detectives launched a criminal investigation into allegations of child sexual molestation after a report was made to the child protective services unit of the Surry Department of Social Services. Authorities concluded that the twins had been sexually abused for the previous seven years, starting when they were 6.

Deputies found a videotape of the girls naked during a search of Smathers’ house, and although he denied touching them, he can be heard narrating the tape, according to a U.S. attorney who prosecuted the Surry man. Court documents allege that Smathers forced the pair to perform sex acts on him in addition to photographing and videotaping them.

As a result of four search warrants being executed, Smathers was charged with two counts of felony child abuse along with two drug-related felonies, manufacturing marijuana and maintaining a drug vehicle. He also was accused of misdemeanor violations of failing to safely secure a firearm from a minor and possession of drug paraphernalia.

The sex-related charges later were moved to federal court due to the crimes being committed with equipment that had been shipped from out of state.

Smathers had agreed to plead guilty in the case at a September hearing, leading to his recent receiving of the 18-year term from Judge Thomas D. Schroeder. Smathers could have received a sentence ranging from 15 to 30 years. Upon his leaving federal custody, he will be on supervised release for the rest of his life.

When arresting Smathers in September 2007, Surry authorities suspected he might have victimized other girls beyond his Westfield-area community, which led to him being charged with nine sexual offenses involving two other girls in Forsyth County. Those incidents allegedly occurred in the late 1970s and early 1980s, including one count of second-degree rape of one girl.

Smathers has not been tried on the Forsyth County violations.