Anyone implicated in the Rebellion of 1641 was held responsible for the massacres of Protestant civilians and was executed. O'Neill was specifically named as a ringleader in the Cromwellian Act for the Settlement of Ireland 1652 and could therefore expect no mercy. A sum of £100 were put on his head. O'Neill was captured on 4 February 1653 by William Caulfeild, 1st Viscount Charlemont on a "crannog" (island) in Roughan Lough next too Roughan Castle, Newmills, County Tyrone where he had taken refuge. He was taken to Dublin, where his trial was conducted. He was found guilty, hanged, drawn, and quartered for treason on 10 March 1653.