The only detailed information about William is from Thomas of Monmouth, a Benedictine monk and a member of Norwich Cathedral's Priory, which took possession of his relics.

Encouraged by the bishop, he appears to have interviewed surviving witnesses of the event and claimed to have obtained inside information about Norwich's Jewish community.

His account is set out in The Life and Miracles of St William of Norwich (Vita et Passione Sancti Willelmi Martyris Norwicensis).

Bishop de Turbeville and other members of the local clergy attempted to create a cultus around him as a Christian martyr, but this plan did not succeed.

There was no evidence in the initial accusations against local Jews that the murder was related to religious activity of any kind, but as the cult developed, so did a story of how and why William was killed.

Theobald alleged that the murder was a human sacrifice and that the "ancient writings of his fathers" required the yearly killing of a Christian on Good Friday.

This was allegedly for two reasons: to one day return to the Holy Land during the Messianic Age and to punish Jesus Christ for the religious persecution that the Jewish people continued to experience at the hands of his followers.

[8] While there is no such commandment for human sacrifice anywhere in Jewish theology or Rabbinic literature, Theobald further alleged that William's murderers were heretics according to the standards of conventional Orthodox Judaism.

"[9] If Thomas of Monmouth's claims about the case were accurate, however, both Jewish and Christian records and chronicles in Southern France would have made at least some mention of a violent messianic cult based at Narbonne.

But in process of time, as I became acquainted with the glorious display of miracles which the divine power carried out through the merits of the blessed martyr William, I became much afraid, and following the dictates of my conscience, I forsook Judaism, and turned to the Christian faith.

[15] Monmouth devotes most of his book not to the murder, but to the evidence for William's sanctity, including mysterious lights seen around the body itself and miraculous cures effected on local devotees.

Monmouth admits that some of the clergy, notably the Prior, Elias, were opposed to the cult on the grounds that there was little evidence of William's piety or martyrdom.

[15] Historian Paul Dalton states that the cult of William was predominantly "protective and pacificatory" in character, having similarities to that of another child saint, Faith of Conques.

[19] As a result of the feelings generated by the William ritual murder story and subsequent intervention by the authorities on behalf of the accused, the growing suspicion of collusion between corrupt sheriffs and nobles and Jews fuelled the general anti-Jewish and anti-Norman mood of the population.

After Thomas of Monmouth's version of William's death circulated a number of other unsolved child murders were attributed to Jewish conspiracies, including Harold of Gloucester (d. 1168) and Robert of Bury (d. 1181).

This, in conjunction with the increase in national opinion in favour of a Crusade, and the conflation of all non-Christians in the Medieval Christian imagination, led to the Jewish deputation attending the coronation of Richard in 1189 being attacked by the crowd.

In 1853, an author attributed William's death to a conspiracy of "the Jews, then the leading doctors, merchants and scholars of the day", and that they escaped then punishment.

Noting Thomas of Monmouth's use of testimonies to construct a consistent account, James argued that these were inventions or were unreliable, or were manipulated to fit the story.

James maintained that the murder's ritual nature emerged only after a man named Theobald, keen to ingratiate himself with the Christian community, promoted the idea.

[3] In 1984, Canadian Medievalist Gavin I. Langmuir endorsed a theory that the murder was a sex crime, probably perpetrated by the self-described "cook", noting that Thomas of Monmouth's account would imply that William's body was naked below the waist.

[32][a] Writing in 1938, Jacob R. Marcus commented on the legacy of William of Norwich and other alleged cases like his: "Generations have believed that no Christian child was safe in Jewish hands.

The Papacy has frequently denounced this charge, yet it is equally true that in numerous instances the accusation of ritual murder was not made except with the vigorous support of local Church authorities.

In the specific case of William of Norwich, the evidence, critically sifted, leads one to believe that he actually existed and that his body was found after he had died a violent death.