SEOUL, South Korea — Prosecutors in South Korea confronted a retired Supreme Court chief justice on Friday with accusations that he conspired to delay a case that could upset relations with Japan, interrogating him in a closed-door hearing that is likely to lead to an unprecedented indictment.

No former or sitting chief justice in South Korea had ever been summoned as a criminal suspect until Yang Sung-tae, 71, presented himself to address allegations that he had manipulated the case on behalf of the nation’s disgraced former president.

The scandal involving Mr. Yang has drawn intense interest in South Korea, where a mistrust of the judiciary is a longstanding phenomenon. The depth of anti-judiciary sentiment is such that when a quixotic pig farmer angry over a court ruling threw a firebomb at the car of the current chief justice, Kim Myeong-su, the November incident received outsize news and social media coverage.

Mr. Yang’s scandal is also being closely watched by diplomats because of its connection to the growing diplomatic schism between South Korea and Japan, both key American allies.