The group was under the leadership of Collins . The names of those who carried out Collins ' orders on the morning of 21 November 1920 were not disclosed until author Tim Pat Coogan mentioned them in his book on the history of the IRA , published in 1970 . Coogan identified Lemass as taking part in the killing of a British agent as a member of " Apostles " entourage that killed fourteen and wounded five British agents of the Cairo Gang . That day , 21 November 1920 , became known as Bloody Sunday
Bloody Sunday
Bloody Sunday (1920)
Seán Lemass