As the Department of Justice prosecutes alleged manipulation of the foreign currency spot trading market, a trio of London-based foreign currency traders who worked for Citicorp, Barclays, and JP­Morgan Chase agreed earlier this month to come to New York in July for their arraignments.

But why face federal prosecution in the Southern District of New York, when U.K. investigators gave the traders the all-clear, and their lawyers have said the U.S. could lose an extradition fight?

Given the stakes, including potential prison time if found guilty, the defendants’ voluntary trip to New York raises questions, according to another white-collar criminal defense lawyer who doesn’t have a client in the case.

“There has got to have been something backdoor brokered to have them submit to the [New York federal court's] jurisdiction without a fight,” said Philip Hilder of Hilder & Associates in Houston, whose past clients include Sherron Watkins, a former vice president for Enron.

But one of the trader’s defense lawyers offers an explanation. “Richard is flying to the U.S. voluntarily, without any need for lengthy extradition proceedings, because he is innocent and wants to conclude this matter on the merits in a U.S. court,” said Michael Kendall, a partner in the Boston office of White & Case who represents Richard Usher.

Usher, a former trader for a Chase affiliate, was indicted in January on one count of conspiring to fix prices and rig bids for U.S. dollars and euros. The indictment, signed by antitrust division prosecutors in New York and by since-fired U.S. Attorney Preet Bharara, also named ex-Citi trader Rohan Ramchandani and former Barclays trader Christopher Ashton.

According to White & Case’s Kendall, the government is proceeding without jurisdictional authority and despite British investigators finding nothing to prosecute.

“British authorities thoroughly investigated the trading in foreign exchange and concluded that there was no evidence to warrant bringing charges against Richard or any of his co-defendants,” Kendall said in an email. U.S. prosecutors, he wrote, “brought this case based on a novel legal theory, as it asserts the Sherman Act applies extraterritorially to conduct that took place in London.”

Hilder disagreed.

“It appears that the indictment does state jurisdictional grounds for the matter to be brought because the transactions occurred within the Southern District of New York. So this is no different theory than what the same U.S. attorney’s office has done by bringing a multitude of securities cases with the jurisdictional arguments being the trades went through New York,” Hilder said.

Southern District prosecutors “do have an expansive view of jurisdiction, but the courts have traditionally upheld it,” he added.

The January indictment came after Citi, Barclays and JPMorgan pleaded guilty to conspiring to fix prices in 2015 and paid criminal fines of more than $2.5 billion. The traders face prison sentences of up to 10 years, as well as potential fines.

Anjan Sahni, a partner at Wilmer Cutler Pickering Hale and Dorr who represents Ramchandani, and David Schertler, a partner at Schertler & Onorato who represents Ashton, did not respond to requests for comment.