As machine gun fire crackled around the besieged Islamist encampment in eastern Cairo today, a 12 year-old boy called Omar was sat on a mattress drinking from his carton of orange juice. Just a few yards away, the bodies of 31 protesters lay on the grubby, blood-caked floor.Many had been shot through the head and chest with high velocity bulletssome bore gnarled lips betraying the agonising throes of death.