After being arrested at Fethard while vested for Mass on Holy Saturday, 25 March, 1654, Fr. Tirry was taken to Clonmel Gaol (on the future location of the Clonmel Borstal) and held there pending trial. Three men had reported his whereabouts to the priest hunters in return for the £5 bounty. On 26 April, he was tried by a jury and a panel of Commonwealth judges, including New Model Army Colonel Solomon Richards, for violating the Proclamation of 6 January 1653, which defined it as high treason against the Commonwealth of England for priests to remain in Great Britain or Ireland. Edited by Patrick J. Cornish and Benignus Millet (2005), The Irish Martyrs, Four Courts Press, Dublin. Pages 178-180. Like all other British subjects tried for the same offence prior to the Treason Act 1695, William Tirry and his codefendant, Capuchin Friar Matthew Fogarty, were forbidden the services of a defence counsel and were forced to act as their own attorneys.Hale's History of Pleas of the Crown (1800 ed.) vol. 1, chapter XXIX (from Google Books).
