Prime Minister Fumio Kishida is facing a dilemma as he investigates a funding scandal within the ruling Liberal Democratic Party (LDP).
The scandal involves the practice of collecting proceeds from ticket sales to the Abe faction's fund-raising parties and returning money to individual faction members that went beyond their ticket sales quotas.
Kishida has questioned four top officials of the Abe faction, who mentioned former Prime Minister Yoshiro Mori as a potential source of information.
Mori, who retired as a lawmaker but still wields considerable influence, is said to have designed the post-Abe group leadership scheme for the faction and named the five top officials who would be included in that circle.
Some of those questioned have also said the fund-return practice went as far back as two decades, when Mori served as faction head.
Kishida has said that he wants to hand out disciplinary measures over the accumulation of unreported money from fund-raising parties sometime next week.
However, the new testimony presented by those from the Abe faction puts the prime minister in a dilemma.
The opposition parties have insisted that Mori be called before the Diet to answer questions about his role in the practice, but the LDP has been reluctant to go along.
If Kishida does question Mori, he may feel the wrath of the faction, especially if new information emerges that leads to further investigations by prosecutors.
Despite retiring as a lawmaker, Mori, 86, still wields considerable influence in the political world.
If Kishida fails to uncover new information from Mori, the opposition would likely criticize him for attempting to cover up what really happened.