President's Commission on the Assassination of President John F. Kennedy, The Warren Commission Report, New York, St. Martin's Press, 1992, p. 110., ISBN 0-312-08257-6.
«The first congressional session after the assassination of McKinley gave more attention to legislation concerning attacks on the President than had any previous Congress but did not pass any measures for the protection of the President. Nevertheless, in 1902 the Secret Service, which was then the only Federal general investigative agency of any consequence, assumed full-time responsibility for the safety of the President.»