Diana and her younger half-brother, Mark Eugene Yoli, were last seen on their way to the playground at Camp Lejeune, North Carolina at approximately 3:15 p.m. on September 13, 1962. Her stepfather and Mark's biological father, a Marine Lance Corporal, was stationed on the base. The children's parents were initially not concerned when they didn't return to their home in the 700 block of Butler Drive, because they were known as adventurous children who tended to wander. An extensive search of the area, lasting four days, turned up no sign of either Mark or Diana.

Convicted child molester Henry Morris Hunt, who died in 1991 at the age of 85, is the only suspect in the children's presumed abductions. On her deathbed in 1992, Hunt's wife told her daughter that Hunt had dumped Mark and Diana's bodies in a mine shaft near Maysville, North Carolina. Hunt reportedly told his wife that he'd picked up the children at Midway Park and taken them fishing, and Mark accidentally drowned and he panicked afterwards and killed Diana. In 2011, bones were found underneath the demolished home once owned by Hunt, and authorities thought they'd found the children's remains, but the bones turned out not to be human.

Mark's date of birth is January 9, 1960; he was two years old at the time of his disappearance. He has dark brown hair, brown eyes, a stocky build and an olive complexion. He was last seen wearing a t-shirt and brown shorts. His photograph and additional information for him are unavailable. Mark and Diana's cases remain unsolved and foul play is suspected.