One of the three churches bombed on Sunday in northern Nigeria by Boko Haram, triggering reprisal killings. Olu Ajayi/AP hide caption

itoggle caption Olu Ajayi/AP

Onlookers view the wreckage of a car bomb that exploded outside a church near Madalla, Nigeria on Christmas Day, 2011 killing scores of people. Boko Haram claimed responsibility for the attack. Sunday Aghaeze/AP hide caption

itoggle caption Sunday Aghaeze/AP