Federal authorities are reportedly focusing on taped phone calls between J.P. Morgan Chase (JPM) employees as officials build criminal cases in the wake of the banking giant’s London Whale trading debacle.

According to The New York Times, four former members of the London team responsible for the $6 billion loss are under legal scrutiny and arrests could be made in the next several months.

To make their case, investigators are scouring over phone conversations, email and instant messages and notes where employees openly discussed how to value the wrong-way trades, the paper said.

They are looking for information on how some traders influenced market prices as their bets soured and into whether records were falsified to hide the problems from New York execs, the Times reported.

J.P. Morgan first disclosed the trading debacle at its Chief Investment Office in May, setting off a decline in the bank’s share price and raising questions about its risk management.

However, the investigation does not appear to touch on Ina Drew, who oversaw the CIO, and could further insulate CEO Jamie Dimon from further fallout, the paper said.

Instead, the Times reported that the attention in focused on four individuals: Javier Martin-Artajo, who oversaw the trading strategy in London; Bruno Iksil, the trader known as the London Whale; Achilles Macris, who led the international chief investment office; and lower-level trader Julien Grout, who was in charge of marking the trading book.

Meanwhile, J.P. Morgan’s C-Suite continues to experience a turnover in the wake of the London Whale scandal.

Chief Financial Officer Douglas Braunstein, 51, is expected to step down and is likely to transition into a different job at the bank, The Wall Street Journal reported. Braunstein’s role was diminished after the July executive shakeup that caused him to report to Matt Zames, the co-chief operating officer, instead of Dimon.

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