Last September, Luigi Mangione’s lawyers told a New York state judge in a sealed court filing that they were considering arguing that their client was experiencing extreme emotional disturbance at the time he was accused of the brazen assassination of a health care executive in Midtown Manhattan.

In the nine months that followed, Mr. Mangione’s lawyers kept the judge, Gregory Carro, informed on their potential approach to the case through sealed communications and in hearings closed to the public. The filing’s existence, and the glimpse it offered into the defense’s strategy in a high-profile criminal prosecution, remained secret until this month, when Justice Carro ordered it unsealed.

In response, Mr. Mangione’s lawyers said they were withdrawing the filing and were no longer considering that defense. The judge ordered the filing and related documents again placed under seal.

As Mr. Mangione’s case has progressed in State Supreme Court in Manhattan, with his trial scheduled for Sept. 8, the secrecy shrouding filings and hearings concerning the defense’s strategy has been in stark contrast to the surge of public attention that seems to accompany Mr. Mangione’s every court appearance.

At a hearing this month, Justice Carro finally explained in an open court session that the confidentiality was necessary while the defense considered the emotional disturbance option, which could involve admitting some responsibility for the crime.

“Because of the nature of that defense, of course, if they didn’t go forward, it would be very prejudicial,” Justice Carro said.

State and federal judges regularly have to weigh requests for confidentiality from defendants and prosecutors against the public’s right to access to court proceedings. In Mr. Mangione’s case, his lawyers have argued that public attention surrounding his case has only increased the need to protect his right to a fair trial.

While the killing of the health care executive, Brian Thompson, on Dec. 4, 2024, sent shock waves through the country, it also set off a groundswell of support for a man who many believed had committed an act of protest.

Since Mr. Mangione’s arrest, supporters have written to him in the Brooklyn jail where he is being held and have donated to his legal defense fund, which has raised more than $1.5 million, according to its website. They show up in large numbers at his court appearances, reporting their observations on blogs and in videos.

The intense public interest in the case has put a spotlight on how in New York’s State courts it can at times be difficult for the public or the press to learn even the most basic facts about a case. Mr. Mangione is also facing charges in federal court in Manhattan.

“This government system relies on the public’s faith that it’s operating in a fair way,” said Rebecca Roiphe, a former assistant district attorney who teaches legal ethics and criminal law at New York Law School.

She said transparency generally reassures the public about the process, and “even if they don’t agree with the result, they have faith that proper procedures were followed and this person was given a fair chance.”

The Supreme Court and other courts have affirmed the right of public access to proceedings in criminal cases.

And Justice Carro has appeared to be mindful of the level of interest in Mr. Mangione’s case. During pretrial hearings in December, at the request of news media, he directed the parties to create an online Dropbox to make evidence available to the public. And twice, Justice Carro allowed cameras into the courtroom to film pretrial hearings.

In federal court, where documents are typically filed on a publicly accessible online docket, Mr. Mangione’s proceedings have been easier to follow. For 10 cents per page, the public can find scores of legal filings. Of the roughly 140 entries listed as of Monday in Mr. Mangione’s federal case, about a dozen are shown as sealed.

By contrast, in the New York State courts, there is no public-facing docket online in criminal cases. Motions and other documents filed by the parties are sent to a judge’s chambers and are made available through an ad hoc system that can differ from judge to judge.

In Mr. Mangione’s case, only a selection of court documents can be found in the clerk’s office on the 10th floor of the Criminal Courts Building on Centre Street. They sit in about a dozen Manila folders inside a banker’s box labeled “Mangione.”

Paul Shechtman, a longtime New York defense lawyer and former prosecutor who lectures at Yale Law School, said the First Amendment recognizes that the defendant and prosecutor each have a strong interest in court proceedings. “But so does the public,” he said.

When court proceedings are hidden, Mr. Shechtman said, “You say: ‘Why? What’s going on that can’t be made public?’”

“Lack of transparency breeds conspiracy theories,” Mr. Shechtman added, “which there’s already enough of.”

Mr. Mangione has pleaded not guilty to state charges of second-degree murder and weapons-related counts. In federal court, he has pleaded not guilty to stalking charges in Mr. Thompson’s killing and is to be tried on them after the state trial ends.

In the state case, Mr. Mangione’s lawyers have partly addressed the lack of access to public documents by creating a website where they regularly post their court filings, the judge’s orders, portions of court transcripts and their own public statements.

The Manhattan district attorney’s office regularly makes its own filings in the case available to the news media.

Lin Weeks, a senior staff attorney for the Reporters Committee for Freedom of the Press, said judges must hear objections if they decide to close courtrooms or restrict information. The judge should make a record of the reason for closing a courtroom, he said, which has to be “overridingly important and as narrow as possible.”

In Mr. Mangione’s federal case, the judge, Margaret Garnett, made such a record in a recent hearing. After a short delay at the start of the proceeding, Judge Garnett entered and announced she had met privately with the defense lawyers to discuss issues related to the defense’s strategy in Mr. Mangione’s state and federal cases.

“I recognize there’s a presumptive public right of access to criminal proceedings,” Judge Garnett explained from the bench, but she added that “the interests in keeping those matters confidential so as to ensure effective assistance of counsel trump the public’s interest in disclosure at this time.”