According to a Vanguard report, the $15m cash which was seized by South African authorities was part of the recovered loot of ex head of state Sani Abacha.
The CBN have established that the $15 million cash was ferried by the office of the NSA for the purchase of arms in the country.
Part of the Abacha loot was also used to secure the services of mercenaries and guerrillas from some countries to assist in re-taking 22 Nigerian territories in the North-East from Boko Haram, Vanguard added.
The government at the time had engaged some of the foreign fighters to train troops in anti-terrorism warfare, intelligence gathering and counter terrorism which enabled them recover the lost territories from the insurgents.
In spite of that, it never admitted using any of them for any of its operations, the report said.