Judge Breyer pointed to the testimony of Zac Nesper, a Hewlett-Packard employee responsible for its foreign exchange trading. As a government witness, Mr. Nesper admitted that he “was not entirely truthful with Barclays,” and that he had understood that what Barclays was “posturing” rather than being “entirely honest.”

Crucial to Judge Breyer’s decision was the fact that the bank was not acting as a fiduciary or agent of the company, nor did it have any duty to protect its interests. Barclays was acting like any other participant in the foreign exchange market by hedging its position before undertaking the transactions on behalf of Hewlett-Packard. So when it sought to profit ahead of the trades, it was simply using the sharp-elbowed tactics of any trader in the market.

Because neither side expected the other to tell the truth, there was no fraud. Fraud cases require some deception, but if you expect that you will not be told the truth, then you cannot be misled.

By taking the rare step of dismissing the case before it reached the jury, Judge Breyer sent a strong message to the Justice Department that business tactics that benefit one side are not always fraudulent, even if a defendant makes silly statements in chat sessions.

The mail and wire fraud statutes are broad and can encompass a number of questionable business practices if one party is misled about the value of an asset or the terms of an agreement. But when it comes to the negotiation of a deal, the courts have taken a hands-off approach if one side makes statements that are not truthful.

In United States v. Weimert, a 2016 decision by the federal appeals court in Chicago, the judges reversed the conviction of a former bank official who had misled both sides about his potential involvement as an investor in a property deal. The appeals court explained that “buyers and sellers negotiate prices and other terms.”

“To state the obvious,” it added, “they will often try to mislead the other party about the prices and terms they are willing to accept. Such deceptions are not criminal.”