While politicians and diplomats formulate their responses, the challenge now for businesses in Manhattan and around the world is to draw lessons from this most terrible chain of events.
Until 11 September, the word "disaster" in disaster recovery conjured images of power cuts, of storms bringing down phone lines, of burst water mains flooding datacentres.
But this was disaster in the truest sense of the word.
Companies must now revisit the concept of business continuity with renewed purpose and urgency. How inadequate the phrase sounds, how tasteless even, in the light of last week's events. Yet business continuity can mean more than simply keeping shareholders happy.
Glib talk from employers about companies being surrogate families to their staff normally jars. But when Howard Lutnick, chief executive of broker Cantor Fitzgerald, a company with 700 staff feared dead in the World Trade Centre attack, talked about remaining in business, he revealed a motivation that was movingly personal.
"There is only one reason to be in business - we have to make our company be able to care for 700 families," he said.
Many of the companies affected by the disaster in the US will have had contingency plans in place. Mission-critical employees will have decamped to remote sites hosting back-up systems; mobile phones and pagers will have replaced regular methods of communication; and members of staff will have assumed tasks normally outsourced to third-party companies.
Chillingly, though, for companies such as Morgan Stanley and Cantor Fitzgerald, the problem was not simply one of lacking premises, but also of lacking the staff with which to populate them.
Some expertise in dealing with events such as occurred last week would have come from the frantic Y2K contingency planning of two years ago.
Nevertheless, this week there were whispers that some companies in Manhattan had insufficient
back-up in place. Many businesses in London and elsewhere around the world, fearing related attacks, will have been unnerved to discover how ill-prepared they were, even for the disruption caused by an office evacuation.
Four years to the day before last Tuesday's tragic events, Computer Weekly ran a prescient story about disaster recovery in New York. Under the headline "NY IT blues", the story reported on forecasts of the chaos that might ensue across the city, should the millennium bug disrupt transport systems, power supplies, telecoms networks and financial services.
If the millennium bug threat did not offer a loud enough alarm call to the corporate world to address its ability to remain in business in the face of disaster, then events in the US must.
By learning from them, we can at least salvage a sliver of consolation from this tragedy.