Banjo was accused of being a coup plotter against Nigerian Prime Minister Abubakar Tafawa Balewa by the government of Aguyi Ironsi.

[6] Three days after Aguiyi-Ironsi came to power, Banjo was summoned to the office of the Supreme Military Commander and was arrested while he was still waiting to see the head of state.

When Biafra was proclaimed on 30 May 1967, Banjo was released from an Eastern Nigerian prison by President Odumegwu Ojukwu and promoted to colonel.

After Banjo was repulsed at the Battle of Ore, he and other officers (Emmanuel Ifeajuna, Phillip Alale, and Sam Agbam) were accused of plotting a coup against Ojukwu.

[8] After a hurried trial,[9] that some authors characterized as biased,[10] they were found guilty of treason and sentenced to death.