Traders from BGC, a global brokerage company in London's Canary Wharf financial centre react as European stock markets open early June 24, 2016 after Britain voted to leave the European Union in the EU BREXIT referendum.Traders from BGC, a global brokerage company in London's Canary Wharf financial centre react, as European stock markets open early June 24, 2016 after Britain voted to leave the European Union.REUTERS/Russell Boyce/File Photo
US prosecutors accused three former London currency traders of arranging a "conspiracy" to rig the foreign exchange markets.
Richard Usher, who worked at both Royal Bank of Scotland and JPMorgan, Rohan Ramchandani, a former Citi banker, and Christopher Ashton, who used to be at Barclays, were charged with "conspiring to fix prices and rig bids for US dollars and euros exchanged in the FX spot market," the DoJ said in a statement.
According to the indictment, from 2007 to 2013 the traders were part of a group that called itself "the Cartel" or "the Mafia," which communicated via phone, messages and chat-rooms to collude on the setting of benchmark FX rates known as the fix.
They tried to manipulate the fix by "refraining from entering orders or trading at certain times," the DoJ said. 
"Today’s indictment reiterates our commitment to holding individuals accountable for corporate misconduct." "Whether a crime is committed on the street corner or in the corner office, no one gets a free pass simply because they were working for a corporation when they broke the law," said Deputy Attorney General Sally Q. Yates.
Stephenson Harwood's Sara George, representing Chris Ashton, said:  "He complied fully with what he understood to be the legal and compliance requirements of an English Bank."
"The UK Serious Fraud Office conducted a thorough and independent investigation lasting over one and a half years and involving in excess of half a million documents," George said in an emailed statement. "A detailed review of the evidence led the SFO to the conclusion that the alleged conduct, even if proven and taken at its highest, would not meet the evidential test required to mount a prosecution for an offence contrary to English law."
The charges follow fines of more than $2.5 billion levied on RBS, Barclays, JP Morgan and Citi in May 2015 after the banks pleaded guilty to conspiring to rig the FX market.
"These former bank traders are alleged to have gained an unfair advantage on their counterparts by committing corporate fraud involving the manipulation of the foreign currency exchange,” Paul Abbate, assistant director of the FBI's Washington office, said in the statement. "Their actions affected worldwide trading positions in the global marketplace."
The action against the three traders takes the number of individuals charged in the US FX probe to six. 
In July last year, two FX executives were charged with conspiring to defraud a client by front-running, which involves trading ahead of a large order to take advantage of the upcoming price move.  This month, another trader was charged with attempting to manipulate emerging market currency rates.