Since the beginning of its war in Gaza, Israel has been hunting one man in particular – Hamas chief Yahya Sinwar. For a year, Israeli soldiers have used drones, radar and ground troops to try to find him, while in Gaza the death toll among Palestinians grew unimaginably in the conflict Sinwar helped to ignite. Then came the news he had been killed. How could his death change the conflict in the Middle East? Julian Borger reports.