Unidentified assailants have set fire to the headquarters of Egypt's runoff presidential candidate Ahmad Shafiq and thousands of protesters have returned to Cairo's Tahrir Square to rally against alleged injustice in the election process. An annex in Shafiq's headquarters in Cairo went up in flames late on Monday, hours after election officials announced that the former prime minister, a symbol of Hosni Mubarak's rule, would square off against Brotherhood's Mohammed Morsi.