DiJulius III, John R.
Secret service: hidden systems that deliver unforgettable customer service
[American Management Association, ], 2003
 eBooks
Toohey, Brian
Oyster: the story of Australia secret intellegence service / Brian Toohey
William Heinemann Australia, 1989
 Buku Teks
Letters from a Secret Service agent: F.L. McDougall to S.M. Bruce, 1924-1929
edited by W.J. Hudson and Wendy Way
Australian Government Publishing Service, 1986
 Buku Referensi
Graham
French
 Buku Teks
Christopher, Paul
Michelangelo's secret
Dastan Books, 2006
 Buku Teks