Co-worker: Rex Heuermann once unnerved her by tracking her down on a cruise: "I told you I could find you anywhere"

This story originally aired on Sept. 16, 2023. It was updated on June 15, 2024.

Not far from a quiet stretch of Gilgo Beach on Long Island, New York, investigators uncovered the hidden remains of four young women. The mystery of who they were and how they got here might have stayed a secret if not for a woman named Shannan Gilbert.