Complex sentence: Seeing this as opportunity of saving lives of Jews in ghettos, Jewish organizations from Switzerland, had start sending documents to Warsaw Ghetto--but, in many cases, the holders of affidavits and passports were already dead.
Split into simpler sentences: Seeing this as an opportunity to save the lives of Jews in the ghettos, Jewish organizations from Switzerland started sending documents to the Warsaw Ghetto. However, in many cases, the holders of these affidavits and passports were already dead.