Kammala jumla mai zuwa: An nada shi mai koyar da ilmin lissafi a 1929, kuma babban malami bayan shekaru shida. A watan Afrilun 1940, yayin da yake ziyartar surukansa a Copenhagen, an kama Kerrich a cikin
Nazi mamayewa kuma an tsare shi a Hald Ege, Viborg, Midtjylland. Yayin da yake can ya gudanar da gwaje-gwaje masu sauƙi ta amfani da tsabar kudi da ƙwallon ping-pong don nuna ingancin ƙwarewar wasu ka'idoji na asali na yiwuwar.