On the afternoon of Monday, 10 September 2001, Karen Lynn Seymour told her boss that she wanted to attend a conference the next morning. The 40-year-old technology specialist at a subsidiary of ICAP, a London-based bond broker, thought it could help her career.

Her boss, Chris Ferreri, said he was less interested in the event, to be held at Windows on the World, a restaurant on the 106th floor of the World Trade Center’s North Tower.