Ilan Goldenberg counts the ways. It seems that when a Shiite kills a Shiite (as happens frequently in the south) that doesn't count. Similarly, when a Sunni kills a Sunni, that doesn't count. Nor does it count when the death was caused by a car bomb since, obvious, well, um, I couldn't even say. The exclusion of Shiite-on-Shiite and Sunni-on-Sunni violence seems like a clever-if-underhanded exploitation of critics' tendency to deploy the phrase "sectarian violence" even though there's a lot of politically motivated violence that isn't sectarian in nature. The car bomb exclusion seems entirely unprincipled.