Garnet's trial took place on Friday 28 March 1606. He was taken to the Guildhall by closed coach; an unusual method, considering prisoners were usually walked to trial, though the authorities may have had some concern about support from a sympathetic crowd. The trial began at about 9:30 am and lasted all day. In attendance were King James (hidden from public view) and several courtiers including Lady Arbella Stuart and Catherine Howard, Countess of Suffolk. Garnet was introduced with his various aliases, which included "Whalley, otherwise Darcy, otherwise Roberts, otherwise Farmer, otherwise Philips". He was accused of having conspired with Catesby on 9 June 1605 to kill the king, his son, and to "alter and subvert the government of the kingdom and the true worship of God established in England". He was also accused of having conspired with several others to blow up the House of Lords with gunpowder. He pleaded "not guilty".