Although aware of the increasing danger that he and his family were in, Loewner was still in Prague when the Nazis occupied the city. Loewner was immediately put in jail and he spent a week there trying to leave the country.
Kahit na alam ng pagdaragdag ng panganib na siya at ang kanyang pamilya ay sa, Loewner ay pa rin sa Prague kapag ang mga Nazis abala ang lungsod. Loewner ay agad-agad ilagay sa bilangguan at siya na ginugol sa isang linggo may sinusubukan mong umalis ng bansa.