The apparent suicide of a key suspect in the Daejang-dong land development scandal has set back a prosecution probe seeking to get to the heart of it.

The scandal centers on allegations that the city of Seongnam, Gyeonggi Province, south of Seoul, gave a few certain civilians special favors so they could obtain astronomical returns on investments in a land development project when Lee Jae-myung, the ruling Democratic Party of Korea’s presidential candidate, was mayor of the city.

Yoo Han-gi, former head of the development business division of Seongnam Development Corp., was found dead near his home Friday after leaving a will at home. The corporation, a public enterprise wholly owned by Seongnam City, was in charge of the project to develop the Daejang-dong district.

Yoo was scheduled to face a pretrial detention hearing on Tuesday concerning allegations that he accepted 200 million won ($167,000) in bribes from two civilian investors affiliated with Hwacheon Daeyu, the asset management firm involved in the Daejang-dong project, in August 2014, in exchange for lobbying the Han River basin environment office.

Lee Jun-seok, leader of the main opposition People Power Party, said something to the effect that Yoo died because the prosecution had investigated all the suspects except the project’s No. 1 architect.

His remarks are valid. With public uproar mounting over the scandal, the prosecution unwillingly launched investigations late in September. It gave up trying to find a suspect’s mobile phone, which was thrown out a window just before the authorities searched his residence. However, the police found it later. The prosecution raided the Seongnam municipal building several times, but skipped over the mayoral office. It searched the office about a week later amid criticism. Prosecutors left Lee Jae-myung untouched, even though as mayor of Seongnam he had the final say over the project.

Yoo Han-gi was regarded as the second-most influential person in the corporation -- behind Yoo Dong-gyu, the former head of the planning division, who has been indicted and is being held in detention.

Yoo Han-gi was being investigated by the prosecution about an allegation that he was involved in Seongnam Development chief executive Hwang Moo-seong’s resignation. This allegation was not included in the prosecution’s request for his pretrial detention. In a transcript of recorded conversations between the two that Hwang disclosed Oct. 24, Yoo Han-gi, who was Hwang’s subordinate, urged the chief executive to tender his resignation. He said Yoo Dong-gyu and Jeong Jin-sang, then the Seongnam mayor’s policy chief, had given the orders to do so. When Hwang showed his displeasure, Yoo made it clear that Mayor Lee himself had given the orders. The transcript raises suspicions that Mayor Lee and Jeong were pulling the wires behind Yoo Han-gi in order to coerce Hwang to step down.

The investigation of Yoo Han-gi should have started earlier. The project was already in full swing after Hwang resigned. The prosecution should have investigated this aggressively, but dragged their feet -- probably to avoid extending the dragnet to the highest official overseeing the project.

Referring to Yoo’s death, Lee Jae-myung said it happened while prosecutors were beating around the bush. He also said a special counsel should be appointed as soon as possible to find out the truth.

Lee Jae-myung talks as if he had nothing to do with the project, though it is obvious that he must have signed off on important documents. After Hwang stepped down, Yoo Dong-gyu, regarded as a figure close to Lee Jae-myung, pushed ahead with the project in earnest as the acting chief executive.

It is hard to find sincerity in Lee Jae-myung’s call for the appointment of a special counsel. The Democratic Party refused to table the opposition party’s bill on the special counsel’s probe to the standing committee. The ruling party has also ignored the People Power Party’s demand for a consultation on the appointment.

Voters should have the full picture before heading to the polls. However, investigations seldom get to the heart of the matter. Yoo’s death, which has set back the investigation, shows that a special counsel is needed more than ever.