I am guessing that these law clerks are familiar with the constitutional protections provided by Fourth Amendment and with 5 U.S. Code § 6385 - Prohibition of coercion of employees, even if some of the Supreme Court justices are not. If the culprit is among these suspects, I am sure they are smart enough not to incriminate themselves.
Chief Justice John Roberts has ordered the Court's marshal to conduct an internal investigation, but there has been no official update, and no indication whether the probe is ongoing, ended or suspended.
But multiple sources tell Fox News the investigation into the approximately 70 individuals in the court who may have had access to the draft opinion has been narrowed. Sources say much of the initial focus was on the three dozen or so law clerks, who work directly with the justices on their caseload. Fox News had previously reported those law clerks were asked to turn over their cellphones and sign affidavits. It is unclear whether those clerks have all cooperated.
Supreme Court law clerks work on a one-year contract for individual justices, and their term typically ends in mid-July. Most of the law clerks have now presumably moved on to other jobs, and any future cooperation with them into the leak investigation was seen as problematic.