A farkon 1940, Maris ya fara aikin shiri, kamar yadda ya kuma shirya wani ɓangare na gyare-gyaren sansanin soja a waje da wasanni na wasanni, ma. Ya zuga binciken binciken kayan tarihi kuma ya gayyaci masanin tarihin gine-ginen Jamus Daniel Krencker don nazarin binciken. A cikin iyakokin fadada Nazi na manyan ayyukan, da haɓaka rawar Jamus da mahimmancin tarihi a wannan yankin, Krencker ya yaba aikin Maris a matsayin "mafarkin fasaha, wanda ke wakiltar wani abu mai mahimmanci na al'adun Jamus wanda zai ba da gudummawa ga tsohuwar ɗaukakar Jamus na Belgrade". 'Yan kwanaki bayan da masana kimiyyar Jamus suka bar sansanin, Jamus ta kai wa Yugoslavia hari a
Ranar 6 ga watan Afrilu, 1941. An tura rukunin wasannin Olympic a gefe, yana mai da hankalin Jamusawa kan binciken kayan tarihi na sansanin a lokacin yakin.