Hilbert was last seen in Cincinnati, Ohio on March 13, 1988. He was on spring break from college at Morehead State University in Kentucky at the time. He left a note for his parents saying he was going to visit some friends at the Ohio State University campus in Columbus. He has never been heard from again.

On April 1, Hilbert's black 1984 Ford Tempo with the Ohio license plate number 807 JPF was found in a desert area in the Beaver Dam Wilderness, in Arizona near the Utah border. Someone had tried to push the car off a cliff, but it got caught on a tree. The front and rear tags had been removed and were never found. Some of Hilbert's belongings were scattered in the vicinity, but there was no sign of him.

Hilbert is considered to be missing under suspicious circumstances. His case remains unsolved.