A day after charges were announced in the 40-year-old kidnapping and slayings of two sisters from Maryland, investigators are turning their attention to the suspect's uncle and others they say were involved in the crime and subsequent cover-up.

At a Thursday news conference in Virginia, police said they believe 70-year-old Richard Welch sexually abused at least one of the Lyon sisters. Twelve-year-old Sheila and 10-year-old Katherine Lyon were abducted from a suburban Maryland mall in March 1975. Their bodies have never been found.

Richard Welch remains a person of interest in the case but has not been charged. His wife, Patricia Welch, has been charged with perjury. Their nephew Lloyd Welch is charged with the girls' murder.

Richard Welch's attorney did not immediately return a message.