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.
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.