He learned about his Jewishness through his father Diego Nuñez da Silva, who was a Jewish physician. Francisco studied the scriptures while he was a medical student.
His skills were so renowned that he became the physician to the leading families in the town of Cordoba, some four hundred miles to the south. An office oflhe Inquisition had been established in Buenos Aires and its agents scoured the continent in search of Marranos (Jews converted to Chris-tianity under pressure) whose Christianity had lapsed or who maintained Jewish practices. The Inquisition’s representatives grew suspicious of Diego Nunez and imprisoned him in Tucuman in 1601. together with his elder son. who told his jailers that his father had instructed him in the laws of Moses and rejected Christianity. The younger son, Francesco Moldano, who was nine years old at the time, had received no Jewish upbringing but was deeply impressed by his brother’s declaration, which sowed for him the first seeds of religious doubt.
In 1605, Diego Nunez was “reconciled” with the Church and received a comparatively light sentence; due to the shortage of doctors, he was released and sent to Callao (today in Peru). Here his younger son, secretly taught by his father, fervently accepted Judaism while outwardly remaining Catholic. He was greatly influenced by the second of the Ten Commandments, which forbade the worship of graven images, and saw Christianity as breaking this command. Under his father’s direction, he too became a doctor and after Diego Nunez’s death in 1616, he worked as a surgeon in a hospital in Santiago de Chile.
At the same time, he began to observe Jewish rituals and, when his wife was absent, secretly circumcised himself. He tried to convert his two sisters but they betrayed him to the Inquisition. They said he had fasted from time to time, pul on a clean shirt on Saturdays, and had questioned the chastity of the Virgin Mary. In 1627, he was imprisoned in Lima. At his first interrogation he spoke proudly of his adherence to Judaism; the next time, he recited the Jewish morning prayers; and at the third audience he declared that Jesus preached magic and then read from his notebook the dates of all the Jewish festivals. When the 55-point accusation was read out to him, it was indicated that he would be treated mercifully if reconciled to the Church. His reaction was to accept all the accusations, and he asked his accusers to add some more, including fasting in prison on the Day of Atonement. He refused to swear on the cross and insisted on swearing in the name of the God of Israel.
Fifteen theological debates ensued in which the inquisitors tried to shake his faith and convince him of the truth of Christianity. He answered their arguments, frequently having recourse to the Bible, and maintained his Judaism. By 1634, after seven years in prison and an eighty-day fast to atone for his sins, he was so weak that he could not turn in bed. Despite his weakness, he succeeded one night in getting out of his cell but instead of making his escape from prison, he entered the dungeons of the other prisoners and actually persuaded two of them to adopt Judaism.
In 1638, the debates recommenced as the Inquisition could not tolerate his dying impenitent. He remained unyielding and presented two books that he had written on the subject while in prison. He also stated categorically that all arguments pertaining to the messianic nature of Jesus were null and void. The Inquisition then saw no alternative to executing him at an auto-dafe at Padregal (Peru). His books were tied round his neck and to the last moment priests tried to persuade him to recant. He was burnt at the stake and his ashes cast to the winds.