MEXICO CITY/NEW YORK (Reuters) – Preliminary findings of a probe by Citigroup’s Mexican unit, Banamex, into how it lost more than $500 million in a corporate loan fraud differ markedly from the results of a separate investigation by the Mexican banking regulator. Banamex has zeroed in on Jose Ortega, a middle manager the bank fired in 2012, as a key person in the fraud involving Mexican oil pipeline maintenance company Oceanografia, according to two people familiar with its probe. The real problem was with the bank’s institutional failure to have proper controls in place, the CNBV says.