Riley was last seen at 1:30 p.m. in the parking lot of a Wal-Mart at 621 Montara Road in Barstow, California. He was accompanied by Mark Adamson at the time and they were getting into an American model, maroon sedan, possibly accompanied by another individual. Neither man has ever been heard from again. Adamson's roommate told police that Adamson left with Riley to buy a vehicle. Adamson reportedly had a large amount of cash on him.

Authorities believe that Riley and Adamson may have been murdered as the result of a drug transaction, and that their bodies are buried in the Mojave Desert. Authorities have a suspect, who has never been identified for lack of evidence connecting him to the missing men's cases. Riley and Adamson have not been located, however, and their cases remain unsolved.