Riegel was last seen in Yakima, Washington on December 25, 2009. He saw his mother that day and spoke to several friends and relatives on the phone. He promised to attend a family gathering the next day, but never showed up. His girlfriend stated they argued and he became upset and left his house 1500 block of South 12th Avenue. He has never been heard from again.

Riegel formerly worked as a contract pilot for Cubcrafters, but his pilot's license had been suspended due to his recent neck surgery and he was unemployed at the time of his disappearance. He had lived in Yakima his whole life and frequented several area bars, including Max's, Boomer's, the Old Town Pump and the James Gang Tavern. Prior to his disappearance, Riegel was in almost daily contact with his family and friends; none of them have heard from him since Christmas 2009. He also hasn't accessed his bank accounts or used his phone. His case remains unsolved.