CHARLESTON COUNTY, S.C. (WCBD) – Authorities say a doctor and former substitute teacher in the Charleston area has been arrested in connection with a 2018 sexual assault of a teenager.

According to Andrew Knapp, a spokesperson for the Charleston County Sheriff’s Office, Robert Dewayne Williams was arrested by the US Marshals Service in Jefferson County, Alabama on Wednesday.

Charleston County detectives opened the investigation on April 4, after the victim reported the sexual assault ,which happened in May 2018.

“In 2018, Williams had been tutoring the victim, a 14-year-old boy, after they met while Williams was substitute teaching at the teenager’s high school,” Knapp said. “The victim, now 18, told deputies that he was assaulted by Williams after they had watched a movie together in a theater.”

According to an affidavit, following the movie, Williams allegedly drove to an unknown location in West Ashley where he turned off the car and began showing the teen “different ways to check his pulse.”

It also alleges Williams then slipped his hands into the teen’s pants and engaged in unwanted sexual activity.

Detectives said Williams had served as a substitute teacher from 2017 to 2018 at various elementary, middle and high schools throughout Charleston County and in Berkeley County.

“At the time, he was a medical student at the Medical University of South Carolina,” Knapp said. He also worked as a pediatrics resident at a hospital in St. Louis.

Williams is being charged with second-degree criminal sexual conduct with a minor 11 to 14 years of age. He is awaiting extradition to Charleston County.

Anyone with information about Williams that could be pertinent to the investigation are asked to call the Charleston County Sheriff’s Office at 843-743-7200 and ask to be connected to a detective.