Wallen rented a 19-foot pleasure boat in Fort Myers, Florida on December 31, 1998. When he hadn't returned it by 5:00 p.m., its owner reported the overdue boat to the Coast Guard. The boat was later found in the Gulf of Mexico, about 53 miles southwest of Sanibel Island. There was no sign of Wallen at the scene and he has never been heard from again.

Authorities believe Wallen was with a woman on the day he disappeared, but there is no description for her and she remains unidentified. Wallen had lived in Florida for about a year prior to going missing. He was staying at a hotel in North Fort Myers at the time he vanished. His case remains unsolved.