Columbia subject headings:
Harvard subject headings:
Informers--Portugal--History--20th century.
Internal security--Portugal--History--20th century.
Political persecution--Portugal--History--20th century.
Polícia Internacional e de Defesa do Estado (Portugal)--History.
Portugal--History--1910-1974.
Princeton subject headings:
Informers--Portugal--History--20th century.
Internal security--Portugal--History--20th century.
Political persecution--Portugal--History--20th century.
Polícia Internacional e de Defesa do Estado (Portugal)--History.
Portugal--History--1910-1974.