A retired Supreme Court justice may soon become a key subject in a widening prosecution investigation into alleged power abuses by the top court's leadership under former chief Yang Sung-tae, informed sources said Wednesday.

Fresh suspicion surrounding former Supreme Court Justice Lee In-bok adds to a ballooning scandal that the top court's administrative body devised detailed plans to curry favor from the presidential office Cheong Wa Dae and win approval from then-President Park Geun-hye of Yang's plan to set up a new court of appeals. 

Some 410 reports written in 2015 by the National Court Administration revealed ways as to how to use some of the most politically sensitive trials as bargaining chips in its dealings with Cheong Wa Dae.

The documents suggested the top court interfered in the trials by pressuring judges to deliver rulings that benefit Park's office.

Lee was the lead judge in one such case in 2012. He upheld a ruling in May that year in favor of Korean victims of Japan's forced labor during World War II, seeking compensation from Mitsubishi Heavy Industries and Nippon Steel & Sumitomo Metal Corp.

But in the course of its reappeal, he allegedly took a self-contradictory stance in the deliberation. A senior judge who had worked with him on the case recently told prosecutors that Lee told him to re-examine his ruling, saying, "The Korea-Japan relations depend on it."

Prosecutors said they have another witness telling a similar testimony about Lee's dubious acts at the time. Prosecutors will verify their statements before deciding whether to pursue the next step against Lee, including a formal summons. Lee is currently a professor at the Judicial Research & Training Institute.

Meanwhile, two other outgoing top court judges implicated in the scandal expressed regret in a joint retirement ceremony held at the top court earlier in the day.

Justices Ko Young-han and Kim Shin said they are "sorry" that the judiciary is under public scrutiny over the allegations and take responsibility for causing concern to the public. Neither of them made any direct comments about themselves in relation to the scandal.

"It's extremely difficult for judges to fulfill their duties when judicial authority has been undermined," Ko said. "We cannot let our dignity fall any further. ... The cases I took will eventually earn praise and criticism in the future, and I believe it's the weight I must carry." (Yonhap)