 They hid with a Polish woman, Maria Sawicka, a member of "Żegota", who before the war had run track with Regina, and who had previously hidden Klepfisz when he had left the Ghetto.During the Warsaw Ghetto Uprising, Klepfisz directed the underground production of explosives for the Jewish resistance.After receiving instruction from the Polish Home Army ("AK") in making Molotov cocktails, Klepfisz set up an underground bomb factory in the Ghetto, while other members of the Jewish resistance smuggled in the necessary ingredients from the "Aryan side" (they had to be purchased from many unrelated suppliers so as not to raise suspicions).