Soper last contacted his family on June 7, 1974. He said he was in Sacramento, California at the time. After graduating from college, he began been traveling around the country with truck drivers. He has never been heard from again. On June 8, 1977, three years later, Soper's clothing and wallet were found in Needles, California. Few details are available in his case. Tulsa, Oklahoma police are assisting the investigation.