The conviction of two British traders for rigging interest rates will stand after a U.S. judge found a key witness’s testimony wasn’t tainted by a related U.K. probe, a decision that could help smooth the way for American prosecutors using evidence gathered in cross-border probes.

Anthony Allen and Anthony Conti, both former U.K.-based Rabobank Groep traders, had argued that their convictions should be overturned because the U.S., in preparing its own case, relied upon evidence they were compelled to give under British law to authorities in the U.K.

U.S. District Judge Jed Rakoff in New York, who presided over their trial last year, said Thursday that federal prosecutors had already separately developed a “significant” amount of evidence independent of the U.K. investigation to charge both men with a scheme to manipulate Libor, an interest rate benchmark.“In light of this substantial documentary evidence and testimony, the court finds fully credible prosecutors’ affidavits stating that they had identified Allen and Conti as potential targets through means unrelated to any exposure to defendants’ compelled testimony,” Rakoff said.

Both Allen and Conti, who plan to appeal, face as many as 10 years in prison when they appear in federal court in Manhattan for sentencing in March.

The case stemmed from a broad U.S. government effort to police global financial markets by targeting industrywide collusion to rig Libor, the London interbank offered rate, a benchmark tied to more than $350 trillion of loans and securities. The trial was the culmination of a seven-year investigation that sparked actions by regulators and enforcers across the globe.

But the decision may have even broader ramifications if U.S. prosecutors now find it easier to use evidence gathered in cross-border investigations.‘Broad Reach’Thursday’s ruling upholds the U.S. government’s “broad reach” in global investigations, said Bruce Maffeo, a former federal prosecutor who is now at Cozen O’Connor in New York and isn’t involved in the Libor case. “I don’t see prosecutors shrinking back.”

The convictions in New York in November came in the first U.S. trial for rigging the rate. Jurors found that Allen and Conti, who both worked in Rabobank’s London office, joined in a four-year scheme to provide submissions for a daily Libor poll that could shift the rate to benefit their trading positions.

Rakoff held a separate hearing in December to determine whether evidence collected by British investigators had tainted the U.S. case. Allen and Conti argued that the government’s star witness, former Rabobank trader Paul Robson, had been influenced in his testimony in the U.S. case by having read 300 pages of statements the defendants had been required to give under U.K. law during a parallel investigation in London. Robson is one of three former traders who struck plea deals with the U.S. in exchange for their testimony against Allen and Conti.

In upholding the convictions on Thursday, Rakoff rejected the claim that Allen and Conti didn’t get a fair trial.

The situation could come up again in a cross-border probe by the U.S., because the Constitution doesn’t allow prosecutors to force people to testify against themselves -- or to use evidence obtained that way.

“We respect the Court’s decision though naturally we are disappointed with it,” Tor Ekeland, a lawyer for Conti, said in a statement. “Mr. Conti plans on pursuing all viable issues on appeal”

Michael Schachter, a lawyer for Allen, didn’t immediately return a voice-mail message left at his office seeking comment on the decision. Peter Carr, a spokesman for the U.S. Justice Department, declined to comment.‘Substantial’ EvidenceRakoff said there was “substantial” evidence and testimony that the U.S. had already identified Allen and Conti as targets of the government’s probe “through means unrelated to any exposure” to testimony that Allen and Conti gave to U.K. authorities conducting their own investigation into the rigging of Libor. The judge also concluded there was “no overlap between the great bulk of Mr. Robson’s trial testimony and defendants’ compelled statements” to U.K. regulators.

Rakoff said letters between U.K. and U.S. investigators showed that the American officials were warned not to review information gathered by British regulators and that the evidence showed Robson had been instructed by his attorney not to share any information he’d learned from the U.K. probe with American authorities.

“Notwithstanding the happenstance that Mr. Allen and Mr. Conti were not indicted until after the start of Mr. Robson’s cooperation, they would likely have been indicted in any event,” Rakoff said.‘Uncharted Territory’The ruling applies only to this case, but it’s the first to address what is likely to be a recurring legal question: whether American prosecutors probing cross-border transactions can rely on evidence gathered overseas in a manner that may violate U.S. laws.

Prosecutors told Rakoff that ruling for the defendants could cripple some cross-border investigations. They said foreign governments seeking to block U.S. probes might seek to compel testimony and make that evidence public so the U.S. would have a harder time building cases.

“A lot of this stuff is uncharted territory,” said James Koukios, a former Justice Department fraud prosecutor now at Morrison & Foerster LLP in Washington. “These were cutting-edge cases where in some ways they were trying to figure out the rules of the road as they went along.”

The U.S. has charged 13 people with manipulating Libor. Four have pleaded guilty. Charges are pending against the others, who aren’t in the U.S.

The case is U.S. v. Allen, 14-cr-00272, U.S. District Court, Southern District of New York (Manhattan).