For this series, Efrem Zimbalist Jr., was provided with an FBI identification card that had a recent photograph of him, fingerprints from his Army service, and an identification number that was only one digit less than a genuine number.
F.B.I. memos, which were recently released under the Freedom of Information Act, have revealed that the real F.B.I. had a veto over casting for guest stars on the series. According to the memos, actors Robert Blake and Bette Davis were barred from making guest appearances on the series.