Three indicted former traders, all U.K. nationals who worked for major international banks, surrendered Monday to U.S. officials, the U.S. Department of Justice announced. They were indicted in January for conspiring to fix prices and rig bids for U.S. dollars and euros in a foreign currency exchange.

Richard Usher, Rohan Ramchandani and Christopher Ashton were indicted Jan. 10 on one count each of conspiring to restrain trade in the foreign currency spot market by the U.S. Attorney’s Office for the Southern District of New York.

Usher, a former trader with affiliates of The Royal Bank of Scotland; Ramchandani, a former trader at an affiliate of Citicorp; and Ashton, a former trader at an affiliate of Barclays, who were known as “the Cartel” or “the Mafia,” prosecutors say, coordinated trading activity, agreeing to suppress and eliminate competition in the FX Spot Market.

Between 2010 and 2012, $1.5 trillion to $2 trillion in currencies were traded each day, and between $400 billion and $500 billion of euro/U.S. dollar currency pair trades, which the defendants by and large dealt in, according to prosecutors.

An attorney for Usher, Boston-based White & Case associate Yakov Malkiel, said U.K. authorities had already determined the defendants’ actions weren’t illegal.

“The U.S. prosecutors would not have prevailed had they sought to extradite Richard. Richard nevertheless decided to come to the U.S. voluntarily to contest the charges at trial and clear his name,” he said. “He is innocent, and he is confident a U.S. jury will agree with the British prosecutors that he did not break any laws.”

Wilmer Cutler Pickering Hale & Dorr partner Anjan Sahni, an attorney representing Ramchandani, and Washington, D.C.-based Schertler & Onorato name attorney David Schertler, an attorney representing Ashton, could not be reached for comment.

A spokesman for the Southern District U.S. Attorney’s Office could not be reached for comment.