On Saturday 20 January 1973 at 15:08, a male caller with an English accent rang the telephone exchange in Exchequer Street, Dublin, with the following bomb warning: "Listen love, there is a bomb in O'Connell Street at the Bridge". Although the call was placed from a coin box in the Dublin area, the exact location was never determined. The telephonist immediately contacted the Garda Síochána. The streets of central Dublin were more crowded than usual as Ireland was playing the All Blacks at an international rugby match being held that afternoon in Lansdowne Road.
At 15:18, a man leaving Kilmartin's betting shop in Sackville Place noticed smoke or steam emanating from the boot of a red Vauxhall Victor car parked outside Egan's pub facing the direction of O'Connell Street. Its registration number was EOI 1229. About five seconds later the bomb inside the red car's boot exploded, scattering sections of the vehicle and throwing the man to his feet. The explosion was so powerful that it hurled the car's roof over adjacent Abbey Street where it landed in Harbour Place; the right hand rear hub and axle sections were blasted through a metal grill on a shop window.
A CIÉ bus conductor, 21-year-old Thomas Douglas, originally from Stirling, Scotland, was passing the betting shop just as the bomb went off and the force of the blast hurled him through a shop front window where he died minutes later of shock and hæmorrhage from the multiple injuries he received in the explosion. The entire shop front was devastated and spattered with blood. Fourteen people were badly injured in the bombing which caused bedlam as hysterical Saturday afternoon shoppers sought to flee the area in panic and confusion. The carbomb detonated at almost the exact location of 1 December bomb. Later eyewitness accounts suggested it had been parked at the kerb several hours before it exploded. According to journalists Jim Cusack and Henry McDonald in their book UVF, the bomb was designed to cause widespread chaos and alarm throughout the city, and to inflict massive injuries upon shoppers and pedestrians as Saturday has traditionally been the busiest shopping day of the week for Dubliners.