A convicted child sex offender who is currently in jail says a 10-year-old girl and her older sister who had gone missing 40 years ago left a Washington, D.C.-area mall with him.

Lloyd Welch, 58, has been named a “person of interest” in the disappearance of two young girls in 1975 from Montgomery County in Maryland, according to a Washington Post report.

Welch allegedly told detectives that he left a shopping mall with 12-year-old Sheila Lyon and 10-year-old Katherine Lyon, and that he later saw his uncle sexually assault one of them, according to unsealed police affidavits as reported by the Post.

It provides the first insight into what happened over the past year to bring the decades-old cold case back to the attention of investigators. So far, neither Welch nor his 69-year-old uncle, Richard Welch, have been charged in connection with the disappearance, and Lloyd Welch said he had nothing to do with their disappearances.

Richard Welch, meanwhile, wouldn’t comment on the allegations, and his daughter said her father would “never do something like that,” according to the report.

The disappearance rocked the D.C. area back in 1975, and the pain only deepened with no signs of what happened to them. Now, detectives may be closer to ending the mystery, albeit not with a happy ending. Detectives believe that the girls were abducted from the shopping mall, and at least one of them was sexually assault before both were killed and then discarded in a remote mountain area far from their home.

Lloyd Welch is currently serving a 30-year sentence in connection a sexual assault on a 10-year-old girl, which he pleaded guilty to in 1998. He also has a sexual assault conviction from 1994.

He claimed that his uncle drove off with him and the girls from the mall.

Last month, authorities announced that they were conducting a “forensic dig” for the girls’ remains on Richard Welch’s land on a Virginia mountain in a rural part of the state 200 miles from where they went missing.