The 1710 apostasy of Samuel ben Jaakow, the Land Rabbi of Lithuania, had no precedent in the history of Polish Jewry. Taking into account the number of Jews in the Grand Duchy of Lithuania at the beginning of the 18th century, he held the most important Jewish office in the federation, if not in the world. The circumstances of his conversion are a mystery. The apostate presented various versions of the events, and any mention of him was removed from Jewish records. Equally puzzling are there his later actions, when he accused Jews of ritual murders, and even confessed having committed them himself when serving as the rabbi. Serafinowicz's testimony made in a Gdansk shelter just before his death shed new light on his apostasy. The former Land Rabbi of Lithuania had no reason to lie on his death bed. He confessed that before his baptism he was imprisoned not by Jews, as he testified earlier, but by his Catholic teachers, who began suspecting him of refusing to convert, contrary to what he declared. It follows from this testimony that the Land Rabbi was forced to convert, and then could not return to the Judaic faith, because apostasy from Christianity was punishable by death in the Republic of Poland and Lithuania.