The decision of the United States Court of Appeals for the Second Circuit in Manhattan in United States v. Newman, which roiled the world of insider trading when it was announced in December 2014, seems to be relegated to little more than a footnote in the history of securities fraud with an opinion from the same court affirming the conviction of Mathew Martoma.

Insider trading law has seen many twists and turns the last few years, and figuring out what is required to prove tipping of inside information meant Mr. Martoma had to wait almost three years for his appeal to be decided.

The law may be settled now with the decision’s finding that the approach in Newman to tipping confidential information “can no longer be sustained.” That is, unless the Second Circuit decides to have all 13 active judges rehear the case, known as en banc review, potentially raising anew questions about what evidence is needed to prove an illegal tip of confidential information.

Mr. Martoma was a portfolio manager at SAC Capital Advisors, Steven A. Cohen’s hedge fund firm that later pleaded guilty to insider trading and shut down. Mr. Martoma obtained confidential information by meeting regularly with Dr. Sidney Gilman, who worked as a paid consultant through an expert networking firm, about a clinical trial of an Alzheimer’s drug.