The prosecution on Wednesday searched the headquarters of the main opposition Democratic Party of Korea in its probe into allegations surrounding a land development project in Seongnam, Gyeonggi Province.

With the latest search and seizure, the prosecution appears to be accelerating the investigation that many watchers expect to ultimately hone in on Democratic Party leader Rep. Lee Jae-myung.

The Seoul Central District Prosecutors' Office raided the home and office of Jeong Jin-sang, vice chief of staff to the Democratic Party chairman. As Jeong’s office is located inside the Democratic Party headquarters, investigators confronted party executives' protest, but eventually entered the headquarters around noon.

The Democratic Party chairman’s secretary office at the National Assembly was also included in the raid target. According to custom, the prosecution met with National Assembly Speaker Kim Jin-pyo before the execution, and Kim suggested voluntary submission considering the symbolism of the National Assembly’s main office.

Jeong is suspected of receiving nearly 140 million won ($102,000) from businessmen related to the Daejang-dong development project. The prosecution secured statements from Yoo Dong-kyu, formerly the Seongnam Development’s planning department head, and Nam Wook, a private developer, that they delivered 50 million won to Jeong around the 2014 local elections. Lee was aiming for reelection as mayor of Seongnam that year. They also claimed to have delivered 40 million won to Jeong in 2020, and several more bribes throughout 2013-2014 and in 2019.

The prosecution suspects that Jeong received bribes in return for providing information about the Daejang-dong development to private developers that he had learned while serving as a high-ranking official in Seongnam and Gyeonggi Province.

The allegation that Jeong had tried to silence Yoo just before the prosecution's search and seizure on Sept. 29, 2021 is also subject to the prosecution's investigation.

After the analysis of the confiscated goods, the prosecution is expected to summon Jeong as a suspect, and expand the investigation to clarify whether Lee was directly involved in the alleged corruption or belatedly recognized the situation.

Jeong has reportedly denied every allegation saying, "The prosecution’s claim that Yoo Dong-kyu gave money to me is worthless fiction."

The Daejang-dong development scandal has been a thorn in the side of Lee since the presidential election campaign, and it has aggregated into an alleged illegal political funds case since the arrest of Kim Yong on Oct. 19.

Ahead of Wednesday's raids, Kim was sent to trial on Tuesday. Kim, the deputy chairman of the opposition party's Institute for Democracy think tank, faces charges of accepting about 847 million won in bribes from private developers while the Democratic Party's primaries for the presidential election were underway.

Kim was in charge of raising funds for Lee’s presidential campaign, and is one of the closest confidants to Lee, along with Jeong.

According to the prosecutors' explanation on Tuesday, Kim had asked Yoo to raise about 2 billion won in funds for Lee's presidential race in February 2021. Yoo said he would scrape up the money from Nam, who earned 100.7 billion won from the Daejang-dong development project. Nam handed over total 847 million won to Yoo across four times between April and August last year.

Kim refuted the prosecution's version of events in a statement on Tuesday. "(The prosecution) is writing a fiction novel to accuse me of being an accomplice within Daejang-dong corruption," he wrote. "I will reveal the truth."

The prosecution suspects that Kim, Jeong and Yoo formed a close relationship with each other in 2010, when Lee was first elected mayor of Seongnam. The investigators believe that after the Daejang-dong project kicked off, they received bribes from private developers, some of which could have flowed into Lee's campaign funds.

So far, Kim and Jeong have denied every allegation, while Yoo issued a decisive statement to the prosecution that led to stronger investigation on Kim and Jeong.

After Kim's arrest, Lee stressed his innocence and defended Kim, claiming the prosecution's probe constitutes clear persecution of the opposition party.

While Lee stayed silent this time, other members of the opposition party strongly criticized the government and prosecution.

"Attempting the search and seizure as soon as the mourning period for the Itaewon disaster ends is the government and the prosecution's concerted efforts to turn public wrath into a political retaliation investigation," said Rep. Lim Sun-suk, at the supreme council meeting Wednesday morning.

Ruling People Power Party’s interim chair Rep. Chung Jin-suk, on the other hand, urged the Democratic Party to cooperate with the investigation, saying, "The prosecution's investigation is finally heading to the core of the Daejang-dong case. I hope (the Democratic Party) will focus on the people's livelihoods instead of trying to defend their chairman," he said via social media Wednesday.