On May 29, the first day of early voting for the June 3 local elections, the rival party candidates for Seoul mayor — the nation's largest battleground — engaged in a flurry of negative attacks. When police carried out a search and seizure related to the collapse of the Seosomun overpass in Seoul, Oh Se-hoon, the People Power Party candidate for Seoul mayor, strongly objected, calling it "blatant election interference backed by power." Jung Won-oh, the Democratic Party candidate, directly hit back at Oh, saying, "The Seoul mayor's post is not a position for building one's presence by fighting the president."
The Seoul Metropolitan Police Agency's Metropolitan Investigation Unit conducted searches that day at seven locations, including the Seoul Metropolitan Government's Urban Infrastructure Headquarters, the headquarters of the prime and subcontracting companies, and on-site offices. The Ministry of Employment and Labor, which set up a separate dedicated investigation team, is also intensively checking whether the design documents were properly followed during construction.
When the news spread, Oh held a press conference at his campaign headquarters in Jongno-gu, Seoul, criticizing it as "a barbaric act of violence that even a dictatorial regime would not have dared." Oh argued, "The reason for unreasonably launching a forcible investigation at a time when full efforts should be made to address the accident is clear," adding that it was "because the 'Myung-pick' candidate's lack of qualifications has been exposed to the whole world." He then warned, "This attempt at a government-backed election to bring down an opposition candidate will invite a fierce backlash."
Jung brought the "safety" issue to the forefront and set himself against Oh. Attending an on-site central election strategy committee meeting held at his campaign headquarters in Jung-gu, Seoul, Jung said, "I will establish safety as the first standard of Seoul city governance," moving to highlight Oh's "responsibility for safety." He pointed out, "Instead of confronting citizens' anxieties and inconveniences, Oh is trying to drag Seoul into the middle of political strife."
A series of complaints also followed. Citing a media report, Jung's campaign filed a complaint against figures on Oh's campaign side on charges of obstruction of business under the Criminal Act and violation of the Public Official Election Act, saying, "Circumstances have emerged showing that Oh's campaign committee produced and systematically distributed content defaming Jung." Jung's side had earlier also filed a complaint against People Power Party lawmaker Joo Jin-woo of Oh's side, alleging the spread of false information. Joo filed a counter-complaint against Jung.
The two candidates also exchanged blows in the first and last TV debate held on the night of May 28. In the leadership-controlled debate, Jung mentioned cases such as the defective construction of the Great Train Express (GTX) and the Seosomun overpass collapse, rebuking Oh by saying, "Oh is insensitive to safety. He still hasn't visited the Samseong Station site." Oh countered, "I will not be drawn into your strategy. You keep using this as election material," adding, "What good would it do for me to go?" During the debate, the two sides also revealed their emotions, with Jung telling Oh "Don't break the rules" when his opponent cut in, and Oh telling Jung "You're lying."
