Robert and Thomas Wintour is written about the Gunpowder Plot is derived from Thomas's confession, signed on 23 November 1605; details of the so-called Spanish Treason were added three days later. One of only two confessions printed in the "King's Book" (a highly partial contemporary account of the affair), Thomas Wintour's was the only account the government had of a plotter who had been involved from the beginning; Guy Fawkes, weakened by days of torture, may have been at the heart of the group, but he was not at its first meetings. However, Antonia Fraser views the document with suspicion, not least because Thomas's
Robert and Thomas Wintour signature, 'Thomas Winter', differs from his normal signature, 'Thomas Wintour' (it was the former that was invariably used by the government). The signature, possibly forged by lieutenant of the Tower of London William Waad, was made only weeks after Thomas had been shot in the shoulder during the siege at Holbeche House. Biographer Mark Nicholls views the difference in signatures as a significant and puzzling lapse, if a "master forger" is presumed to be responsible for the document. He views the handwriting on the confession as "convincingly that of Winter [Wintour]", pointing out that it appears to be the work