She showed him the Great Comet of 1577, writing that he "was taken by [his] mother to a high place to look at it",[1][2] and later a lunar eclipse in 1580.

In 1615, Ursula Reinbold, the wife of a glazier, accused Katharina after a business dispute with her of having given her a bitter drink that had made her ill, and she reported Katharina to the ducal sub-bailiff of the Leonberg office, demanding compensation for the pain she had suffered.

A witch trial was initiated by Lutherus Einhorn who in his reign as Vogt of the Protestant town of Leonberg (1613–1629) accused fifteen women of sorcery and executed eight of them by burning.

He acted in accordance with the will of the government and the public, which had asked for an investigation of sorcery, and issued an arrest of Katharina Kepler in 1615.

Johannes Kepler defended his mother himself, he had sought advice with the assistance from lawyers and theologians of his university of Tübingen.

When she was finally shown the instruments of torture in order to force her to confess, she remained steadfast: "She said that they could do whatever they wanted with her, and even if they pulled out every vein from her body, she would still have nothing to confess ... she would also want to die on that; God would reveal after her death that injustice and violence had been done to her."

Although the witch trial against Katharina Kepler was one of the best-documented cases in Germany, it received little attention in research.

The biography shows that the Vogt of Leonberg ignored the legal requirements from the beginning and acted according to his own interests.