Nigerian President Goodluck Jonathan has sacked his special adviser on counter-terrorism chief Zakari Ibrahim, two weeks after a car bomber killed 23 people at the UN’s headquarters in Nigeriabn, said Nigerian Presidency Spokesman Reuben Abati.Reuben Abati did not give details on why former counter-terrorism Chief was removed. Investigations are still underway on how the bomber of the U.N. headquarters on August 26 was able to breach state security.