The two young siblings, Sheila, 12, and Katherine, 10, vanished from a mall in suburban Maryland in 1975. Forty-two years later, a sex offender pleaded guilty to two counts of first-degree felony murder in the case.
Undated photos of Sheila and Katherine Lyon released by the FBI. Sheila was 12 at the time of her disappearance, and Katherine was 10. FBI/AP Buy Photo