Parties stirred uneasily as the prosecution continued its interrogation of Park Tae-gyu, the key lobbyist involved in the Busan Savings Bank.

Park’s case, together with that of Seoul Educational Superintendent Kwak No-hyun’s bribery allegations, is shaking up the political landscape ahead of the upcoming Oct. 26 by-elections as well as on the general and presidential races next year.

Park turned himself to the Supreme Prosecutor’s Office at the Incheon International Airport on Sunday, five months after he fled to Canada to avoid the probe.

Park is accused of lobbying financial officials and politicians in a bid to keep Busan Savings Bank from being suspended. The bank’s fall in February caused critical economic losses to its depositors, and played a decisive role in bringing a crucial by-election loss to the ruling Grand National Party.

He was also suspected of using his influence in drawing an 100 billion won ($92 million) investment in the bank from Samsung Dream Scholarship Foundation and Pohang University of Science and Technology.

Though he denied the charges, he turned out to have taken more than 1.5 billion won from the savings bank in exchange of his lobbies, according to prosecution officials. “Kim Yang, the former vice executive director of the bank, testified that Park took 1.7 billion won and later returned 2 billion won,” said a prosecution official.

Authorities also suspected that part of the money was delivered to politicians and government officials.

The related investigation made the Grand National Party in particular uneasy as Park is known to have close relationship with several of its key lawmakers.

“Park had connections with all major figures,” said a GNP lawmaker who asked to remain anonymous. “The results of the upcoming elections will depend on who Park will name during the investigation.”

Should Park point at GNP members during questioning, the GNP is expected to face setbacks in next month’s by-elections, especially amid the aftermaths of the free meal plebiscite failure and Seoul Mayor Oh Se-hoon’ resignation.

On the other hand, the main opposition Democratic Party, which faltered upon the bribery allegations of liberal education chief Kwak, raised its voice over the case.

The party referred to Park as the core figure of the Busan Savings Bank corruption scandal and urged the prosecution to investigate the case thoroughly.

“Our party shall keep a close watch on whether Park reveals the name of all those who were involved in the case,” said Rep. Park Jie-won on his Twitter.

The prosecution has so far indicted 64 people in relation to the Busan Savings Bank case, including Eun Jin-soo, the former commissioner of the Board of Audit and Inspection, and Kim Hae-soo, a former aide to President Lee Myung-bak.

By Bae Hyun-jung (tellme@heraldcorp.com)