General Discussion

German authorities required the assistance of the Axis nations and of local collaborators in the regions they occupied to implement the "Final Solution." Collaborators committed some of the worst atrocities of the Holocaust era.

Axis governments, police, and military authorities aided in the roundup and deportation of Jews to killing centers, actively participated in the murder of Jews, and in several cases committed atrocities against their Jewish fellow citizens within their own national borders.
In territories they occupied (particularly in the east) the Germans depended on indigenous auxiliaries (civilian, military, and police) to carry out the annihilation of the Jewish population.

Axis government authorities and local auxiliaries in German-occupied regions were key in implementing expropriation, deportation for forced labor, and mass murder of non-Jewish populations.

https://encyclopedia.ushmm.org/content/en/article/collaboration

Collaboration with the Nazis outside of Germany was extensive and widespread. The Nazis relied on cooperation from countries, groups, and individuals outside of Germany to carry out the persecution and mass murder of Jews, as well as other victims such as Roma , Poles, Slavs and others.

Collaboration took many forms. In some countries the government actively cooperated with the Nazis. In others, individuals or groups acted on their own initiative to offer their help to the Nazis. Smaller forms of collaboration also took place on an individual basis, such as informing on Jewish neighbours (sometimes out of antisemitism, sometimes out of a desire to take over their property, jobs or valuables once they had been arrested or deported).

https://www.theholocaustexplained.org/resistance-responses-collaboration/collaboration-outside-of-germany/