Visit by John Fitzgerald Kennedy
Commissioner Costigan was involved in the security for the visit of then President John F. Kennedy to Ireland in 1963. Three death threats had been received and Commissioner Costigan urged his subordinates not to overlook the possibility of threats no matter how unlikely they were. He regarded the visit as the most important the country had since independence.
Criticism by Charles Haughey
Criticism by Murphy Report
The Murphy Report criticised Commissioner Costigan for his handling of allegations of child abuse by Fr. Edmondus (pseudonym). Scotland Yard had contacted him concerning images that the priest had sent to be developed in the UK. Commissioner Costigan asked Archbishop John Charles McQuaid to handle it because a priest was involved and he claimed "Gardaí could prove nothing".
- Modern Irish lives: dictionary of 20th-century Irish biography, Ed. Louis McRedmond
- A history of the Garda Síochána: a social history of the force 1922-52, Liam McNiffe
- Stepaside for Mark, Kevin Rafter, Sunday Tribune, 27 July 2005, retrieved 11 December 2009
- Ireland Knew of Threats to Kennedy in 1963 Trip, Alan Cowell, December 29, 2008, retrieved 11 December 2009
- Angry Haughey hit out at garda chief, Fergus Black, Irish Independent, 30 December 2008, retrieved 11 December 2009
- Garda connivance in stifling abuse inquiries deplored, Carol Coulter, The Irish Times, 27 November 2009, retrieved 11 December 2009
- Murphy Report, Part 2, Section 13.5