Three former traders at Rabobank -- British, Australian and Japanese citizens -- were charged in the United States for manipulating Libor benchmark interest rates.
The charges come less than three months after the bank agreed to a deferred prosecution deal with the US Justice Department as part of its Libor manipulation probe and agreed to pay a $325 million penalty.
Briton Paul Robson, Australian Paul Thompson and Tetsuya Motomura of Japan, were charged in New York as conspirators in the rate-manipulation scheme.
They were charged with conspiracy to commit wire fraud and bank fraud, as well as substantive counts of wire fraud. If convicted, the men each face up to 30 years in prison for each count.
The three "deliberately submitted what they called 'obscenely high' or 'silly low' Libor rates in order to benefit their own trading positions," said Acting Assistant Attorney General Mythili Raman.
"The illegal manipulation of this cornerstone benchmark rate undermines the integrity of the markets."
In May 2006, Thompson informed Robson that his net exposure for his three-month fixes was 125 billion yen, and then emailed to ask him to "sneak your 3m libor down a cheeky 1 or 2 bp" because "it will make a bit of diff for me."
Robson then replied: "No prob mate I mark it low."
Libor, or the London Interbank Offered Rate, is a global benchmark that is calculated daily, using estimates from banks of their own interbank rates.
It underpins the terms of $500 trillion of contracts from mortgages to the cost of corporate lending.
However, the system has been found to be open to abuse, with some traders lying about borrowing costs to boost trading positions or make their bank seem more secure.
For almost six years between May 2005 and January 2011, Rabobank allowed money market traders to manipulate Libor submissions to benefit foreign currency trading positions, according to prosecutors.