Police on Tuesday questioned an aide of Rep. Park Hee-tae, the National Assembly speaker and a ruling party member, as part of their investigation into the election-day cyber attack against the national election watchdog.

The aide, identified by his surname Kim, is one of five people who had drinks with a main suspect ―- a staffer to Grand National Party Rep. Choi Ku-shik -― the night before the attack.

“We questioned, as witnesses, all five who had drinks with Gong on the eve of the Oct. 26 by-elections,” said sources at the National Police Agency’s cyber investigation unit, which is leading the probe.

“We found nothing as of yet that indicates Kim’s involvement in the hacking,” the sources said.

The Speaker’s office said Kim tendered his resignation Monday.

The main suspect, identified by the surname Gong, is in police custody, accused of directing the cyber attack on the election watchdog with three others, paralyzing the website for about two hours in the early morning of Oct. 26. By-elections took place across the nation that day, including for Seoul mayor, in which the GNP suffered a crushing defeat. He was Rep. Choi’s personal driver until last month.

According to police sources, Gong asked a hometown friend running an IT firm, identified by surname Kang, over the phone to hack into the election body’s website on election day. Kang and two of his employees mounted a distributed denial of service attack, or DDoS. The 27-year-old Gong denies his involvement, while the other three have pled guilty.

Gong made the phone calls to order the cyber attack while he was with Kim and four others, drinking, police officials said.

The five participants of the drinking session, including Kim, all claimed no knowledge of the plan to attack the election watchdog’s homepage. They insisted that there was no mentioning at all of the elections. The case, having implicated two staffers of GNP legislators, is fast turning into a political scandal, as investigators are focusing their inquiries on suspicions that higher-ups in the conservative party may have been involved.

Rep. Choi, Gong’s former employer, resigned as head of the GNP’s public affairs office after the scandal broke out. He had served as the campaign communications director for the GNP’s mayoral nominee, Na Kyung-won, in the Oct. 26 election. Na lost to Park Won-soon, a maverick backed by liberal opposition parties.

Police were looking into bank accounts and phone records of the suspects, trying to determine whether there were more involved. They are also trying to ascertain whether the suspects were behind a similar attack on the same day against the home page of then-mayoral candidate Park.

By Lee Sun-young (milaya@heraldcorp.com)