Civilian Saucer Investigations (CSI) was an independent unidentified flying object research group founded in Los Angeles, California in 1951. Unlike some of the amateurish "flying saucer clubs" of the era, CSI was comprised largely of people with considerable scientific and technical expertise, most notably Ed J. Sullivan of North American Aviation, and rocket expert Walther Riedel. Nonetheless, letters and notes in Ruppelt's personal files note that he considered collaborating with CSI, due to the high levels of training amongst its membership.