Prosecutors have identified former President Moon Jae-in a suspect in a bribery case, alleging that his former son-in-law received preferential treatment in securing a job with an airline in return for arranging a key government appointment for the politician who founded the airline, according to legal sources on Sunday.

The Criminal Division 3 of the Jeonju District Prosecutor’s Office is leading the investigation into Moon's potential involvement, as detailed in a search warrant executed Friday at the home of his daughter, Moon Da-hye.

The raid stems from complaints filed four years ago regarding the hiring of Moon's former son-in-law, Seo, at Thai Eastar Jet, who has since divorced Moon's daughter. The investigation focuses on a possible connection between Seo’s employment and the appointment of former lawmaker Lee Sang-jik as head of the Korea SMEs and Startups Agency or KOSME.

The conservative ruling People Power Party and Seoul-based civic group "Justice People" filed four complaints between September 2020 and April 2021, alleging possible quid pro quo.

In September 2020, the People Power Party, then the main opposition party, filed a corruption complaint with prosecutors regarding Seo's appointment as executive director of Thai Eastar Jet, a low-cost carrier founded by Lee, a two-term lawmaker with the then-ruling Democratic Party and the founder of South Korea's budget airline, Eastar Jet.

Lee was appointed KOSME president in March 2018, just months before Seo joined Eastar's Thai unit in July. Seo's lack of airline industry experience, combined with the company's financial struggles, raised suspicions of presidential office involvement in his appointment.

Prosecutors suspect that Lee's appointment as KOSME chief may have been decided during an informal meeting of presidential secretaries in late 2017.

The prosecution alleges that former President Moon and his wife had been supporting their daughter's family for some time but ceased this support after Seo was hired by Thai Eastar Jet. If the support was cut off after Seo's employment, the prosecution believes that the support from the airline, including Seo's salary and housing, could be seen as a bribe to Moon.

Prosecutors estimate that Seo received a total of 223 million won ($166,500) in salary and relocation expenses to Thailand between July 2018 and April 2020, which they view as bribes to Moon. Accordingly, they indicated in the search warrant that Moon is suspected of receiving this amount as a bribe from Lee.

Seo has been questioned three times this year as a witness, consistently maintaining his right to remain silent.

Earlier, prosecutors booked Cho Hyun-ock, former senior presidential secretary for personnel affairs under Moon, on power abuse charges related to the case, questioning several other former presidential office officials.

Notably, Im Jong-seok, a former chief of staff under Moon, was questioned on Aug. 19. Prosecutors inquired whether he played any role in appointing Lee as chief of the startups agency in 2018. They also questioned Minor Rebuilding Korea Party leader Cho Kuk, Moon's senior aide at that time, for over three hours on Saturday.

The ruling and opposition parties reacted differently to the prosecutors' raid on the home of Moon's daughter.

People Power Party spokesperson Jeong Kwang-jae stated on Saturday, "The Democratic Party and opposition parties consistently argue that all citizens should be equal before the law," emphasizing, "Moon Da-hye is no exception; she must also be held to the same standard."

Critics argue there is a political motive behind the investigation. Confirming his summon via social media, Im suggested the case was initiated by "political prosecutors" aiming for "political purposes," highlighted by recent searches of bank accounts belonging to Moon and his wife.

While entering the Jeonju District Prosecutors' Office on Saturday, Cho alleged the investigation against Moon and his family aims to divert attention from suspicions surrounding President Yoon Suk Yeol and First Lady Kim Keon-hee.

Meanwhile, 37 Democratic Party lawmakers, many former aides from Moon’s administration, condemned the prosecution for labeling Moon a suspect.

At a press conference at the National Assembly on Sunday, they warned, "The ultimate outcome of this political revenge will be the downfall of the current government and the prosecution."

The lawmakers of the Democratic Party denounced the allegations, "Cease the baseless political retribution against the former president. The more the current administration resorts to such extreme measures to navigate their crisis, the greater the public's outrage will be directed at the presidential office in Yongsan."