At 11.53 on Friday morning, Seifeddine Rezgui stood on the beach at Port El Kantoui in Sousse and made a 10-second telephone call on his white Samsung Galaxy mobile phone. The tall, handsome young man knelt down, produced a Kalashnikov AK-47 from within a rolled-up beach umbrella and test-fired a couple of rounds into the sand. Then he began the task of killing Western tourists. Who exactly he had been calling before he began his spree is not yet known. But over the next 47 minutes Rezgui, a 23-year-old student, murdered 38 people, all of them foreign holidaymakers and most of them British: he also shot a Tunisian woman, and then immediately apologised to her. Pursued by hotel employees, all...