An entire floor at the U.S. Court of Appeals for the D.C. Circuit was locked down Friday as judges heard arguments in a sealed case involving a grand jury subpoena that's believed to be linked to the special counsel's investigation.

The lockdown came as a three-judge panel considers a case arising out of a grand jury subpoena fight, suspected to be linked to Robert Mueller's special counsel investigation into Russian interference in the 2016 presidential election. Details about the case—particularly the identity of the party hoping to suppress the subpoena—have been held under wraps.

Judges Thomas Griffith, David Tatel and Stephen Williams heard two other lawsuits Friday morning: one suit addressing the president's financial disclosure reporting requirements and another revolving around individuals who've participated in an annual diversity visa lottery. Once those arguments drew to a close an hour later, court security officers announced a recess and promptly ushered the audience out. Only law clerks were permitted to stay.

Officers cleared not only the room, but the entire fifth floor, where Friday's proceedings were held. For over an hour, a U.S. marshal declined to let reporters pass through the hall, and the court gave no indication as to how long the hearing would last.

The lockdown sent reporters scattering about the courthouse, searching for clues about the case. Sightings of any special counsel prosecutors or other attorneys remained elusive.

Only public reporting and court docket entries have offered clues about the dispute. The subpoena appears to have first been issued to the elusive party in August, with a district judge in D.C. ruling on the matter shortly after. The case then arrived at the appeals court, before it was sent back to the district court, and appealed a second time to the D.C. Circuit.

In the first attempt to bring the challenge to the appeals court, a panel dismissed the case. When the witness sought to have the full bench reconsider the decision, the sole Trump-appointed judge on the court—Greg Katsas, a former Trump White House deputy counsel—appeared to recuse himself. The cloak-and-dagger case was first brought to the public's attention through an October story published by Politico.

The case appears to mirror a separate dispute over a grand jury subpoena involving Andrew Miller, an ex-aide to Trump confidant Roger Stone. In that case, Miller is challenging the legitimacy of the special counsel's appointment in his bid to fend off a subpoena. A separate D.C. Circuit panel heard arguments in November, but hasn't yet ruled.

One floor down Friday, a federal district judge was hearing arguments in a challenge to Matt Whitaker's appointment as acting attorney general. During the more than 90-minute hearing, Judge Randolph Moss appeared skeptical of whether Whitaker's challenger, Las Vegas resident Barry Michaels, has standing to bring the case. But Moss also pressed Justice Department attorney Hashim Mooppan on Whitaker's appointment, saying it was “concerning” to have an official lead the DOJ without being Senate-confirmed.

When asked whether Whitaker had recused himself from the numerous challenges to his appointment, Mooppan demurred, responding that the Justice Department didn't have to make a “representation about whether the acting attorney general is personally involved.”

Mooppan added that Michaels needs to have standing before going on a “fishing expedition” into the happenings at the Justice Department. Toward the end of the hearing, Michaels' attorney, Tom Goldstein, said he was withdrawing his emergency motion for a preliminary injunction to give Moss time to fully consider Whitaker's appointment without deadline pressure.

Moss said he would rule soon but did not give a specific timetable.

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