https://www.rudi-harthoorn.nl/verzet-door-en-vervolging-van-nederlandse-communisten-a-b/
https://archief.amsterdam/indexen/deeds/98533418-5f57-56a3-e053-b784100ade19?person=98533418-5f58-56a3-e053-b784100ade19
Hendrik Berk | Nationaal Archief