THE Archbishop of Dublin, Dr Desmond Connell, said Ms Guerin's murder marked a further descent into terrorism in Dublin which needed to be confronted with determination and vigour.
Dr Norman Gamble, the rector of St Doulagh's Parish, where Ms Guerin lived, expressed his deep sympathies and prayers to her family.
The National Union of Journalists condemned the murder as did the Paris based press freedom group, Reporters Sans Frontieres.
The president of the Garda Federation, Mr Frank Gunne, expressed outrage at the killing.
A spokesman for the Garda Representative Association said the death was tragic and brutal, and the Association of Garda Sergeants and Inspectors expressed revulsion.
Ms Mary Finan, president of the Dublin Chamber of Commerce, said the shooting was a direct attack on democracy.
A book of condolence will open in Liberty Hall, Dublin, this morning and will remain open until tomorrow evening.