JPMorgan Chase has formally revised its first-quarter financial results to show a lower profit, after deciding that traders at its main investment arm had overstated the value of certain derivatives.
The reduction followed the bank's internal investigation into the nearly $US6 billion ($A5.7 billion) in trading losses revealed in recent months.
JPMorgan reiterated that it had discovered that some traders may have tried to conceal the size of losses from a soured bet.
The "London Whale" trades involved complicated hedging strategies intended to reduce the bank's risk, but actually increased it when they backfired.
In a regulatory filing, the New York bank said on Thursday the probe found information that "suggested that certain individuals may have been seeking to avoid showing the full amount of the losses being incurred".
As it revealed last month, the bank now says that it earned $US4.92 billion for the quarter ended March 31. That's $US459 million less than the $US5.38 billion originally reported.
JPMorgan's regulators, the Federal Reserve and the Office of the Comptroller of the Currency, told the bank to restate a measure of capital strength that it had previously published for the first and second quarters. In its filing, the bank revised the measure downward for the two quarters to reflect additional risk from the trading loss.
Since the financial crisis, investors have started paying closer attention to the measure, known as the capital ratio, which reflects the health of a bank and its ability to handle the stresses during sudden financial upheavals or economic uncertainty.
The bank also admitted to a "material weakness" in its internal controls. It said steps have been taken to address the problems, but noted that management is continuing an internal review of the matter.
The huge loss has embarrassed JPMorgan, which made it through the financial crisis with a reputation for taking less risk with its customers' money than other major banks.
CEO Jamie Dimon has been called before Congress to explain the debacle, and regulators in the US and Britain are looking into the loss.
The bank may still face civil fraud charges stemming from filing its original financial statements.
If regulators decide that employee deceptions caused JPMorgan to report inaccurate financial details, they could pursue charges against the employees, the bank or both.