Nigeria, Sept. 21 -- Ahead of Nigeria's 2019 general elections, perennial presidential hopeful, Atiku Abubakar, mounted an intense campaign to untangle his candidacy from a public perception that he is corrupt. This is what his opponents have always latched on to. But in 2019, he decided to confront the question of corruption head-on.

"I have always said that if they have any evidence of corruption against Atiku, please come forward," Atiku told a packed audience in Ado Ekiti, southwestern Nigeria. "But nobody has been able to come forward."

As Atiku made media and public appearances daring detractors to provide evidence against him, American authorities were also busy poring through records to determine if the former vice president had...