US Federal authorities have opened an investigation into a $400 million fraud involving Citigroup’s Mexican unit. Citigroup had disclosed in February it had discovered at least $400 million in fraudulent loans in its Mexico subsidiary, Banco Nacional de Mexico, known as Banamex, and said employees may have been in on the crime. The bad loans were made to Mexican oil services company Oceanografia, a contractor for Mexican state-owned oil company Pemex. The investigation, overseen by the FBI and prosecutors from the United States attorney’s office in Manhattan, is focusing on whether holes in Citigroup’s internal controls contributed to the fraud in Mexico. The FBI and prosecutors are questioning whether Citigroup was equal parts victim and enabler, the newspaper said.