President Buhari's biographer, John Paden in his book ‘Muhammadu Buhari: Challenges of Leadership in Nigeria,’ stated that President Buhari has incriminating evidence against his predecessor, Goodluck Jonathan. In Chapter 20 page 203 of the book, Paden wrote
“As of the early months of 2016, it appeared that the EFCC was not going after Jonathan. Nor was it going after former president Obasanjo.
The question of the stability of the entire political system seemed at stake. In addition, a number of senior military officers who had served as head of state – from Babangida to Abubakar – seemed off limits. Indeed, rumours swirled that if the probes went after senior officers, they might push back, because they had extensive networks in the active military services. At the same time, the knowledge such heavyweights possessed could well be traded for immunity, and would help to illuminate the patterns and sources of corruption. Buhari had letters in his possession showing Jonathan’s requests for off-budget funds. But Buhari’s larger purpose was not to put former high-level officials in jail. Rather, it was to retrieve stolen funds and to change the political culture of the country.”