Prosecutors investigating the judicial abuse scandal surrounding former Supreme Court Chief Justice Yang Sung-tae have summoned a number of current and former senior judges for questioning.

The National Court Administration's former Planning and Coordination Director Lee Min-geol is suspected of having a role in the top court's alleged attempt to trade verdicts for policy favors.

Prosecutors have secured evidence indicating Lee was involved in the Supreme Court's attempt to defer a ruling on litigation filed by Korean victims of Japan's forced labor during World War Two.

Prosecutors also want to know the extent of Lee's involvement in the top court 's alleged collection of 350 million won from district court budgets to distribute among district court chiefs and senior judges as incentives, among other expenses.

The prosecution is also questioning current and former researchers at the top court accused of improprieties such as taking confidential documents from the Supreme Court.