It has been nearly two weeks since the bloody attacks on the Westgate shopping mall in Nairobi, where militants aligned with Somali Islamists, al-Shabaab, emptied guns and tossed grenades on unsuspecting shoppers. Last night, in Mombasa, a car lay on the side of a road, riddled with bullets and with four bloody corpses inside.

I first met Sheikh Ibrahim Ishmael two days before his killing, in the office of Abubaker Shariff Ahmed—nick-named "Makaburi"—a well-spoken, if not radical, debater who is ...