The ongoing investigation concerning former Chief Justice Yang Sung-tae poses two challenges to the country -- restoring public trust in the judiciary and separating politics from the criminal justice system, especially the state prosecution.

The complete truth in the case has yet to be proved, but the undeniable fact is that the prosecution’s investigation of Yang and other former top justices itself has reduced public trust in the judiciary.

Indeed, some described the scene Friday of Yang walking into the state prosecutor’s office to become the first former chief justice interrogated as a criminal suspect as the most shameful moment for the judiciary.

Public frustration runs deep because the judiciary tended to have a higher level of public trust than the executive and legislative branches.

Again, all the allegations raised about what Yang and his top aides at the Supreme Court’s administrative agency did when he headed the top court should be verified. Besides, there is no denying the case is part of efforts of the current liberal government of President Moon Jae-in to punish former conservative governments in the name of correcting “long-accumulated” wrongdoings.

Nevertheless, the fact that Yang faces as many as 40 charges, for which one of his former top aides had been put into custody, points to the possibility that he and his aides did something wrong.

The charges filed against Im Jong-heon, former deputy director of the National Court Administration, range from intervention in trials to abuse of power in personnel affairs of judges. The prosecution believes Yang and two former heads of the NCA conspired with Im to commit the misdeeds.

Heading the charges is the allegation that the court administration colluded with the government of former President Park Geun-hye to delay the deliberation of a civil damages suit filed by Koreans who were taken to Japan as forced labor during Japan’s colonial rule.

The prosecution suspects that Park wanted the court to delay its work because a ruling in favor of the Korean victims could harm Seoul’s relations with the Tokyo government. Prosecutors argue that, for his part, Yang needed Park’s support for his plan to establish a new high court of appeal.

These suspicions remind one of the rulings the court had made in favor of the government during past military dictatorships. Some such rulings, including those concerning pro-democracy activists, have been revoked in retrials.

It is against this backdrop that the allegations against Yang make many suspect that independence and fairness of the judiciary can still be undermined by intervention by senior judges and politicians. Regardless of how the Yang case develops, the Supreme Court ought to devise measures to restore public confidence in the judiciary.

In the meantime, suspicion that the judiciary has its own problems should not justify the excessive, indiscriminate investigation conducted by the state prosecution, which is at the vanguard of digging into the misdeeds committed during the two past conservative governments led by Lee Myung-bak and Park.

Few would deny that some of the investigations into Lee and Park, both of whom are now in jail, and Yang’s case were politically motivated, with the aim of punishing the former conservative ruling elite.

All in all, the case of Yang has huge, complicated implications in many respects. What’s important is that Yang should not be given any privilege for having been a chief justice. Nor should he be discriminated against simply because he led the top court during conservative administrations. The state prosecution should bear this in mind.