A secret whistleblower has assisted the Justice Department in its investigation of the Bank of New York Mellon Corp. which has resulted in civil lawsuits asserting that BNY systematically overcharged investors on billions of dollars of currency trades, defrauding them for over a decade. The suits, which seek more than $2 billion will result in a reward to Grant Wilson, the inside informant who ran a BNY trading desk for the past ten years, buying and selling currency for the bank’s biggest clients. Until yesterday, Mr. Wilson’s identity was a closely kept secret. The bank was giving false currency transaction prices, according to various lawsuits. BNY has denied wrongdoing and is fighting the lawsuits.