He arranged for his squad to assassinate 35 members of the Cairo Gang on the morning of 21st November 1920. Fourteen of the killings were completed successfully.
In response, the RIC and Black and Tans opened fire on the crowd of a Gaelic football match at Croke Park, killing 14 people. Three suspected IRA members were then tortured and killed at Dublin Castle that evening.
All three attacks happened on the same day and the event became known as Bloody Sunday.