The raids are believed to have been planned by Sean Russell who later organised the bombing campaign in England in the 1930s
So, who was Sean Russell? Well, he was a senior member of the IRA. Born in 1901, he died in a German U-Boat 100 miles off the coast of Ireland in 1940. From 1922 until his death he remained a senior member and chief of staff of the IRA, while it divided and was outlawed, and removed itself to the political fringe of Irish society.
The Crown Forces, led by the Auxiliaries (and supported by the ‘Black and Tans’) mobilised in Dublin on the morning of the match with orders to go to Croke Park and search the crowd for known gunmen and weapons. Throw-in for the match was scheduled for 2.45p.m. but when three I.R.A. men, Sean Russell, Tom Kilcoyne and Harry Colley, were informed (by their contacts) of the planned search of Croke Park they came to Croke Park and pleaded with Luke O’Toole, General Secretary of the G.A.A., to cancel the match. O’Toole took the decision not to cancel the match; the mood in Dublin, and the Stadium, was very tense, rumours of the previous nights exploits were circulating amongst the crowd and thoughts of reprisals must have been prominent in peoples minds. O’Toole judged that any announcement to clear the stadium would lead to a panic induced exodus amongst the 10,000 strong crowd and that a crush could develop at the turnstiles.
Born in Fairview, Dublin in 1893, Russell joined the Irish Volunteers in 1913. He participated in the 1916 Easter Rising as an officer in Dublin Brigade’s 2nd Battalion, under Thomas MacDonagh. Following the Rising he was interned in Frongoch and Knutsford. After the Irish War of Independence began, he was attached to the IRA General Headquarters Staff (GHQ) and became IRA Director of Munitions in 1920. In 1925, after the Irish Civil War, he was jailed in Mountjoy Prison but escaped on 25 November in a breakout he helped organise.
http://en.wikipedia.org/wiki/Se%C3%A1n_Russell has a full account of his life
I cannot find anything to substantiate his part in Bloody Sunday