Original sources about this question were not revealed until 1993, when transcripts of secretly recorded conversations among ten top German physicists, including Heisenberg and Weizsäcker, detained under Operation Epsilon at Farm Hall, near Cambridge in late 1945, were published.
Kebenaran tentang masalah ini baru terungkap pada 1993, ketika salinan-salinan dari percakapan-percakapan yang direkam secara rahasia di antara 10 fisikawan paling terkemuka Jerman, termasuk Heisenberg dan Weizsäcker, yang ditahan di Farm Hall, dekat Cambridge pada akhir 1945, diterbitkan.