In the years after 1933, collaboration between the Dutch and German police, as in previous years, was shaped by the conferences of the International Criminal Police Organisation – founded in 1923 partly on Dutch initiative – which was the forum for organising formal and informal collaboration for the largest European (and later) North American police corps. Chiefs of police from major cities exchanged off-the-record information on extremist groups during these conferences.

After the Nazis seized power, the Netherlands did not participate in these conferences for a while. International exchange on police responses to political extremism was, however, resumed in 1934 and led to informal contacts with the German police and the Gestapo.

The archive of the Auswärtiges Amt shows that the Dutch police cooperated with the German diplomatic service and the Gestapo and accommodated requests for information on German citizens. Such information was divulged when someone was a suspected criminal or enemy of the state – usually a communist activist. But information was also supplied on the whereabouts and activities of migrants for no clear reason at all or on the basis of a newspaper article (entries 87-91).

The authorities also gained information on individuals through unofficial channels – usually via personal initiatives. The archive contains various reports from Dutch citizens on suspected political or anti-German activities and attitudes among Germans living in the Netherlands. A case in point is the letter from A.C. Vermout about a German engineer who treated his mother abominably and wrote articles “containing the most appalling slander and allegations against the Führer” (entry 222).

A letter about a book-dealer sent in 1935 by someone working at the Ministry of Propaganda confirms that such reports were taken seriously. As a result of the letter all the books sold by the dealer were placed on the black list (dossier 248).