After attracting the ire of the Catholic Church for stating the Earth orbited the Sun, Italian astronomer Galileo Galilei was put on trial at the Inquisition headquarters in Rome. To avoid being burned at the stake, the 69-year-old was forced to renounce his belief in a heliocentric model of the universe. Nevertheless, the famed polymath still was sentenced to live out his last years under house arrest. As Alison Abbott reports in a Nature News exclusive, a long-lost letter reveals that before Galileo was convicted on “vehement suspicion of heresy,” he already lived in fear of persecution—and was willing to create a fake paper trail in an attempt to fool the Inquisition.

Galileo wrote the 1613 missive to his friend, the mathematician Benedetto Castelli. The original letter, recently uncovered in a misdated library catalogue at the Royal Society in London, is believed to be the first documented account of his inflammatory arguments for the secular pursuit of science, and it includes his support of Polish astronomer Nicolaus Copernicus’ 1543 theory of a Sun-centered universe.

Perplexingly, two versions of the letter are around today: One contains far more passive language about Galileo’s findings; the other, a more inflammatory copy, is what ultimately ended up in the hands of the Inquisition. Researchers have long wondered: Which letter was the original? Was the more cautious one written by Galileo himself, in an attempt to soften his revolutionary beliefs? Or was the more radical one doctored by members of the Inquisition, charging Galileo’s language to build their case against him?