He referred to the medieval historian John of Wallingford as supporting this identification, stating that Wallingford referred to a second Guthrum being active in Edward's reign.
According to the chronicles of John of Wallingford, Sweyn was involved in raids against England during 1002–1005, 1006–1007, and 1009–1012, to revenge the St. Brice's Day massacre of England's Danish inhabitants in November 1002.
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