David Mason was a serial killer who targeted elderly people in the early 1980s. He also left a cassette tape in the possession of his family, who turned it over to the police when they came knocking. This tape had David's confessions on it, with details only the police and the killer could know.
Sources for this episode:
Wikipedia - Statesboro, Georgia, David Mason (murderer), Oakland, California, San Quentin State Prison
Murderpedia - David Edwin Mason