When Major Obasanjo landed at Kano airport on 13 January 1966, nobody met him. Surprised, he continued to the Engineers’ base at Kaduna. Again nobody met him. He telephoned his closest friend, Major Chukwuma Nzeogwu, who promptly ar r ived to take him home, then left for his office, explaining that they were conducting night training exercises: ‘Operation Leopard’. The acting commander of the engineers had left a note telling Obasanjo that he could not take over until 15 January. Obasanjo decided to catch up on his unit's files. The night of 14–15 January was disturbed by explosions and gunfire, but when he woke, everything was silent. Puzzled, he made for army headquarters. Nzeogwu was there, with a bandaged neck wound and his arm in a sling. He had just assassinated the Premier of Northern Nigeria.

The coup d’état had been planned since August 1965, first by young officers in southern Nigeria clustered around Major Emmanuel Ifeajuna, then drawing in Nzeogwu and others in the North. Accounts differ, but there were probably five core conspirators: four Igbo and one Yoruba, including several of the best educated, best trained, and most politically conscious middle-ranking officers in the army. They planned to sweep away the political and military leadership by simultaneous strikes in Lagos, Kaduna, and perhaps other regional capitals. ‘Our enemies’, Nzeogwu proclaimed, ‘are the political profiteers, swindlers, the men in the high and low places that seek bribes and demand ten per cent, those that seek to keep the country divided permanently so that they can remain in office as ministers or VIPs of waste, the tribalists, the nepotists.’