The attacks Attack are said Statement to have resulted in Causation Boko Haram extending Cause_change_of_position_on_a_scale its control Control to over 70 % of Borno State , while its leader , Abubakar Shekau , claimed Statement responsibility for the massacre Killing in a video statement Statement , saying Statement that they `` were not much '' and that the group 's insurgency `` would not stop Preventing_or_letting '' .