WASHINGTON — In March 2021, a year into the coronavirus pandemic, a key witness in a criminal case in a federal court in New York was allowed to testify remotely, from his lawyer’s office in California. The cross-examination was marred by technical glitches and the stilted awkwardness familiar to anyone who has participated in a Zoom call.

The testimony helped convict two defendants of bank fraud. This month, they asked the Supreme Court to decide whether the remote testimony had run afoul of the Sixth Amendment, which guarantees a criminal defendant the right “to be confronted with the witnesses against him.”

The pandemic has made videoconferencing commonplace, and many people remain wary of large gatherings. Remote testimony might appear to be a sensible compromise.

But Jeffrey L. Fisher, a law professor at Stanford, said courts should be cautious.

“COVID has taught us two lessons,” he said. “One lesson is that Zoom is a very good piece of technology that can save lots of time and expense.”

“But coming out of COVID has also taught us that Zoom is not a substitute for in-person interactions,” he continued. “If we think about all the people we’ve met during the COVID era and then finally meet face to face a year or two later, there are all kinds of things you notice and appreciate for the first time, even if you’ve had all these interactions over Zoom. That’s a powerful lesson, too.”

That is a practical point. There is also the matter of the Constitution.

Justice Antonin Scalia, who reinvigorated the Supreme Court’s commitment to the confrontation clause, was deeply skeptical of remote testimony.

“A purpose of the confrontation clause is ordinarily to compel accusers to make their accusations in the defendant’s presence — which is not equivalent to making them in a room that contains a television set beaming electrons that portray the defendant’s image,” he wrote in 2002 when the court rejected a proposed amendment to the Federal Rules of Criminal Procedure that would have made it easier for judges to allow remote testimony.

“Virtual confrontation might be sufficient to protect virtual constitutional rights,” Scalia wrote. “I doubt whether it is sufficient to protect real ones.”

The technology has improved in the intervening decades, and the pandemic gave the question more urgency. But the lawyers for the defendants, Hamid Akhavan and Ruben Weigand, argued that the constitutional principle remained constant. “There is no Zoom exception to the confrontation clause,” they wrote.

The case concerned credit card transactions for marijuana dispensaries. Among the witnesses was Martin Elliott, a Visa executive who was 57 and had hypertension and a heart arrhythmia and also helped care for his mother-in-law. Judge Jed S. Rakoff, of the U.S. District Court in Manhattan, granted the witness’s request to testify remotely in light of his health and family obligations.

Everyone else — the judge, the lawyers, the jurors, court staff and 15 other witnesses — came to court in person. The two sides dispute how important Elliott’s testimony was, but a prosecutor made 42 references to information about Visa in the government’s closing argument.

The defendants were convicted, and the 2nd U.S. Circuit Court of Appeals affirmed under one of its own precedents, United States v. Gigante, which allows remote testimony where “exceptional circumstances” and the “interest of justice” favor it.

Other federal appeals courts take a different view, rejecting Gigante. “The simple truth,” the 11th Circuit said, for instance, “is that confrontation through a video monitor is not the same as physical face-to-face confrontation.”

The Supreme Court has recognized one exception to the general rule that a criminal defendant is entitled to, as a 1970 opinion put it, “challenge his accuser in a face-to-face encounter” in front of the jury. The exception, established in 1990, allowed children who were said to have been sexually abused to testify by video apart from the defendant but in the physical presence of the lawyers cross-examining them.

The vote was 5-4. Scalia, who died in 2016, wrote the dissent, which was joined by three liberal members of the court — Justices William Brennan Jr., Thurgood Marshall and John Paul Stevens. “For good or bad,” Scalia wrote, “the Sixth Amendment requires confrontation, and we are not at liberty to ignore it.”

Courts have long said that there is something different about assessing a witness in the flesh.

More than a century ago, the Supreme Court of Missouri considered what jurors may see in the courtroom: “the furtive glance, the blush of conscious shame, the hesitation, the sincere or the flippant or sneering tone, the heat, the calmness, the yawn, the sigh, the candor or lack of it, the scant or full realization of the solemnity of an oath, the carriage and mien.”

Last year, that same court rejected the 2nd Circuit’s approach and reversed the conviction of a defendant whose trial had included remote testimony.

In their brief in the 2nd Circuit, prosecutors wrote that “the use of two-way video testimony did not violate the confrontation clause.”

But Derek L. Shaffer, a lawyer for the defendants in the case, Akhavan v. United States, No. 22-844, said his clients “had the constitutional right to look their accuser in the eye and to put his testimony to the test in court — not with the witness Zooming from the comfort of his attorney’s offices 3,000 miles away.”

This article originally appeared in The New York Times.