In an early morning chat, three senior currency traders at someof the world's biggest banks weighed the pros and cons of admittinga fourth member to their private instant-message group.

The traders — from Citigroup Inc., JPMorgan Chase & Co. andUBS AG — had worked together for years to manipulate the $5.3trillion-a-day currency market by sharing details of client ordersand coordinating trading strategies, two people with knowledge of aglobal investigation into the foreign-exchange market said lastyear. While adding a new recruit would bolster their strength, theyworried he couldn't be trusted to put the group's interests aheadof his firm's.

“Will he tell the rest of desk stuff,” Richard Usher, JPMorgan'schief London-based dealer, wrote in the chat published Wednesday bythe U.S. Commodity Futures Trading Commission. “Or god forbid hisnyk,” he said, referring to the New York trading desk.