According to Church records, he died on 18 July 838 but other sources give dates between 834 and 838.

At a young age he was taught at Utrecht by the clergy, including Bishop Ricfried.

According to the 11th and 12th century writers Bishop Otbert of Liège (Passio Frederici) and William of Malmesbury, the killers were hired by Empress Judith, because of Frederick's regular criticism of her dissolute way of life.

Later writers like Cesare Baronio and Jean Mabillon write that the inhabitants of Walcheren, who were hostile to Christianity, sent them as a response to Frederick's preaching there.

There are no sources of writers of the time showing that the empress was unchaste or immoral, or that Frederick had made that allegation.