Let’s return to the Chronicles of Saint Gall, a collection of stories that spans 400 years of the abbey’s history, filled with surprising episodes. Among these is the fratricide of Frederick I of Toggenburg in 1226, the youngest son of Count Diethelmo I of Toggenburg from the district of Thurgau, and the brother of Diethelmo II. The latter, driven by envy of Frederick, his co-heir and father of six children, harbored jealousy and resentment toward him, feelings further fueled by his wife Gertrude of Neueburg, whom he married against his father’s wishes.

In an attempt to reconcile the two sons, their father was imprisoned by the eldest, while the mother’s life was endangered, having been struck by an arrow shot by Diethelmo II. In contrast, Frederick is portrayed as the obedient and respectful son: knighted by Emperor Frederick II himself in Cremona, he had married a woman chosen by his father, against the wishes of his sister-in-law Gertrude, who preferred him to marry one of her sisters. This disdain led Gertrude to incite her husband to violence with sly words and manipulations.

Pretending to seek reconciliation with Frederick, the couple invited him to the castle of Rengerswil, where they welcomed him with celebrations for three days. On the third night, while Frederick's guards slept, Diethelmo’s men disarmed his escort and murdered Frederick in his sleep. His last words were pleas for help directed at his brother. However, Diethelmo had already left to seize the deceased’s property, but to no avail. Frederick’s body remained unburied for seven days until the arrival of the abbot of Saint Gall, who received all of Frederick’s possessions from his parents. 

Diethelmo denied any involvement in the murder but failed to convince anyone of his innocence. Accused of being the mastermind behind the crime, he was excommunicated by the bishop of Constance and banished from the royal court. He attempted to wage war against the abbot while at the emperor's court, but his ambitions were thwarted: besieged at Rengerswil, he was forced to surrender and cede his possessions to the Abbey of Saint Gall, securing only a small restitution.