The horrific accident that brought death and injury to the centre of Dublin on Saturday has yet to be explained in a way that is fully comprehensible.
But the scale of the tragedy means that the Dublin Bus and Garda investigations now underway must produce a clear and precise account of the sequence of events involved as soon as possible. Some members of the emergency services described the carnage as possibly the worst they have had to deal with, while eyewitnesses provided graphically shocking accounts of a bus colliding with passengers waiting at a bus stop.
However, in a confined area of Dublin's city quays that is normally crowded with pedestrians and commuters and the suitability of which as a location for a bus stop, it now transpires, has been called into question, it is remarkable that the death toll was not much higher.
The ambulance and hospital services deserve praise for the expeditious and reassuring activation of their accident emergency plan. Sympathy and condolences must go to the bereaved and the injured who - as the Minister for Transport, Mr Brennan, said - will "suffer awful trauma for the coming days, months and years".
The victims were going about the normal business of a Saturday afternoon - innocent bystanders in a public place, awaiting their transport home to the West Dublin suburbs and Kildare. The volume of people who visited the scene yesterday - in some cases placing floral tributes - bore eloquent testimony to the extent to which their loss has touched the wider community.
For Dublin Bus, which has a good safety record, and for all those associated with it, Saturday's events were, as a spokesperson for the company put it, "a dark, dark day".
But among the central issues which must be addressed by the State-owned firm is the extent of its assessment of, and its response to, concerns which - it has now emerged - had been raised with it about security and, to a lesser extent, safety at the location of the accident by councillors from Lucan and Leixlip - the destination areas to which buses travel from Wellington Quay.
Dublin Bus has been quick to state that there were no safety issues associated with the Wellington Quay or other bus stops. Nor, given the nature of its operations, can the company be expected to guarantee an accident-free environment for its customers. However, it is incumbent on it to do everything possible to minimise the risks involved.
Against this background and in order to reassure Dublin Bus customers and the wider public, it is a matter of fundamental public interest that the investigations which are currently under way not only establish the facts of what happened and why it happened, but include also a full review of the safety of all locations around the city where members of the public congregate for public transport. As Saturday's events have so graphically demonstrated, nothing can or should be taken for granted in this regard.