The conspirators were interrogated for three months in the Tower of London. Evidence suggests that Fawkes, who had given his name as John Johnson, was tortured.
The King sent an order to the Tower of London on 6 November 1605 authorising the use of torture on Fawkes, who had initially refused to divulge the names of his co-conspirators. The order is held by The National Archives.
‘If he will not other wayes confesse, the gentler tortours are to be the first usid unto him…God speed youre goode worke. James.’
Although it is not known whether any of the other main conspirators were tortured, it was authorised against some of the more minor figures involved.
Fawkes' signature appears on a confession of 8 November. This confession did not name all his accomplices. The effect of torture upon Fawkes is evident from a more detailed confession on 9 November where his signature is barely legible.
Francis Tresham died of natural causes in the Tower of London on 23 December 1605. The eight surviving conspirators were tried in Westminster Hall on 27 January 1606. All were condemned to death for treason.
Four men - Sir Everard Digby, Robert Winter, John Grant and Thomas Bates - were executed on 30 January 1606 in St Paul's Churchyard.
The other four - Guy Fawkes, Thomas Winter, Ambrose Rookwood and Robert Keyes - were executed just outside Westminster Hall, in Old Palace Yard, the following day.
The heads of the two ringleaders, Percy and Catesby, who had been killed earlier at Holbeach House in Staffordshire, were set up on the 'Parliament House'.