Even a note sent to Heinz secretly by his friend Kurt Cierer has survived. The documentation was rescued and brought to Israel by Heinz's female associates. Today, everything is stored in the Yad Vashem archives.
Legal postal contact with the Terezín ghetto was not easy. Correspondence cards could only be sent through the Council of Elders and were subject to strict censorship, and parcels could only be sent after obtaining a so-called admittance stamp, which entitled the parcel to be sent to Terezín, from the post office in Ostrovní Street reserved for Jews and Jewish affairs.