The militant is known as Abu Ubaida al Masri, and charting his path reveals his vulnerabilities and those of the terrorist group. COPENHAGEN -- If Al Qaeda strikes the West in the coming months, it's likely the mastermind will be a stocky Egyptian explosives expert with two missing fingers. His alias is Abu Ubaida al Masri. Hardly anyone has heard of him outside a select circle of anti-terrorism officials and Islamic militants. He has overseen the major plots that the network needs to stay viable, investigators say: the London transportation bombings in 2005, a foiled transatlantic "spectacular" aimed at U.S.-bound...