A contemporary Portuguese document suggests Buckingham as the guilty party, stating "...and after the passing away of king Edward in the year of 83, another one of his brothers, the Duke of Gloucester, had in his power the Prince of Wales and the Duke of York, the young sons of the said king his brother, and turned them to the Duke of Buckingham, under whose custody the said Princes were starved to death." A document dated some decades after the disappearance was found within the archives of the College of Arms in London in 1980; this stated that the murder "be the vise of the Duke of Buckingham". This led Michael Bennett to suggest that possibly some of Richard's prominent supporters, Buckingham and James Tyrrell, murdered the princes on their own initiative without waiting for Richard's orders. Bennett noted in support of this theory: 'After the King's departure Buckingham was in effective command in the capital, and it is known that when the two men met a month later there was an unholy row between them.' Buckingham is the only person to be named as responsible in a contemporary chronicle other than Richard himself. However, for two reasons he is unlikely to have acted alone. First of all, if he were guilty of acting without Richard's orders it is extremely surprising that Richard did not lay the blame for the princes' murder on Buckingham after Buckingham was disgraced and executed, especially as Richard could potentially have cleared his own name by doing so. Secondly, it is likely he would have required Richard's help to gain access to the princes, under close guard in the Tower of London, although Kendall argued as Constable of England, he might have been exempt from this ruling. As a result, although it is extremely possible that he was implicated in the decision to murder them, the hypothesis that he acted without Richard's knowledge is not widely accepted by historians. While Jeremy Potter suggested that Richard would have kept silent had Buckingham been guilty because nobody would have believed Richard was not party to the crime, he further notes that "Historians are agreed that Buckingham would never have dared to act without Richard's complicity, or at least, connivance". However, Potter also hypothesised that perhaps Buckingham was fantasising about seizing the crown himself at this point and saw the murder of the princes as a first step to achieving this goal. This theory formed the basis of Sharon Penman's historical novel, "The Sunne in Splendour". Henry VII (Henry Tudor), following his seizure of the crown, executed some of the rival claimants to the throne.