The effect is to restore the full legal arsenal at the disposal of prosecutors. Of course, whether they will use it as aggressively as Preet Bharara, the United States attorney in Manhattan whom President Trump fired in June, remains to be seen. (A permanent replacement for Mr. Bharara hasn’t been named.)

Martoma “wasn’t a hard case,” said John C. Coffee Jr., a professor at Columbia Law School and an expert on white-collar crime. “In fact, it’s one of the easiest insider-trading cases I’ve ever seen.” While the appellate panel may have overreached in its eagerness to limit the damage from Newman, he said, the upshot is that “the odds have again swung to the prosecutors’ advantage.”

Both the Newman and Martoma appeals turned on the relationship between the person who conveys inside information (the “tipper”) and the person who receives and trades on it (“the tippee”). To be guilty of insider trading, the tipper needs to personally benefit, directly or indirectly, from the disclosure, the Supreme Court has held.

Until Newman, this benefit was construed quite broadly, and could easily be inferred if the tipper and tippee were relatives, friends or even acquaintances. But in Newman, the Second Circuit held prosecutors to a much higher standard, ruling that the relationship must be “a meaningfully close personal relationship that generates an exchange that is objective, consequential, and represents at least a potential gain of a pecuniary or similarly valuable nature.”

That meant the traders who passed on and traded on inside information in the Newman case went free. (The fact they were business school classmates who had worked together at the same company and known each other for years wasn’t a close enough relationship, the court ruled.) Prosecutors had to dismiss the convictions and guilty pleas of seven people who’d participated in insider trading schemes, in some cases reaping millions in profit, including Michael S. Steinberg, one of Mr. Cohen’s top lieutenants.

That set the stage for Mr. Martoma to argue that he, likewise, had no close personal relationship with Dr. Gilman and that the doctor didn’t reap any gain from disclosing the information.

But the Martoma case proved to be a vivid illustration of a truism about inside information on Wall Street: there are few true gifts. The relationship between tippers and tippees is almost always complicated by personal ties and expectations of future benefits — monetary or emotional or both. Wall Street “operates like a big favor bank,” Mr. Coffee said.