The New York Times reports investigators are focusing on four people who worked for the London team responsible for the loss.
The Times says authorities are also examining notes from staff meetings, instant messages and emails.
The report says the investigation is in the early stages and federal prosecutors haven't decided whether to file charges.
No current or former employee has been charged with wrongdoing.
JPMorgan Chase declined comment.
The bank reports its quarterly earnings Friday and is expected to face more questions about the trading loss.