Regina Hicks was supposed to pick up her 4-year-old son, Montana, from the home of her estranged husband's friend in Willard, Ohio -- but he said she never showed.

Soon after her disappearance on the evening of Oct. 18, 2001, investigators found the 25-year-old's dead body in her white Camaro, submerged in a nearby pond, beginning a decades-long search to unmask her killer.

A new "20/20" episode, " The Secret in the Water " a i ri ng Friday, May 1, at 9 p.m. ET on ABC and streaming the next day on Disney+ and Hulu, examines the case.

You can also get more behind-the-scenes of each week's episode by listening to "20/20: The After Show" weekly series right on your 20/20 podcast feed on Mondays, hosted by "20/20" co-anchor Deborah Roberts.

Regina first started dating Paul Hicks when they were in high school, eventually marrying.…