Riddle was last seen at an acquaintance’s residence in the 23900 block of West Coleman Drive in Congress, Arizona. He left the residence and returned the following morning to collect some personal belongings but has not been heard from since. His vehicle was found on October 19 on a dirt road in the desert near 5 Mile Tank in Congress. Several days later, a pair of his shoes were discovered near the location where his vehicle had been found. Notably, the shoes were located in an area that had already been searched previously.