The prosecution said Wednesday that questioning President Park Geun-hye must take place by Friday, reiterating that she is an essential witness in the investigation into the scandal involving her confidante Choi Soon-sil.

A questioning session with Park was slated for Wednesday, but was postponed after her lawyer said it was “physically impossible” for her client to comply at a press conference Tuesday.

“An investigation tomorrow doesn’t seem plausible at this point. We (prosecutors) said it was necessary to do it today. ... We plan to tell them that if we were to concede beyond the ‘Maginot Line’ (absolute final deadline), Friday would be possible,” a high-ranking official from Seoul Central Prosecutors’ Office said.

Park is suspected of being directly involved in the scandal, which includes allegations that Choi had meddled in state affairs and siphoned off public funds.

The official said that the prosecution remains unchanged on its position that Park will be probed not as a suspect, but as a key witness in the case. This makes it impossible for the investigators to forcibly question her, as it would not be permitted to take her into custody.

If the president chooses not to comply with the prosecution’s questioning, it will be forced to reach a decision accordingly, he said.

Suspicions that Park is directly involved in the Choi scandal have been further fueled in the past few days, with evidence uncovered from her former aides.

The prosecution’s investigation into former presidential secretary An Chong-bum reportedly found that he had received orders from Park about raising funds for the Mir Foundation and K-Sports Foundation. The two nonprofit organizations are suspected of being used as a cover to channel money to Choi.

According to local media outlet Munhwa Ilbo, An’s notebook confiscated by the investigators showed that Park had given direct instructions about the foundations from day one, requesting regular updates on their progress.

It even specified how a company effectively owned by TV commercial director Cha Eun-taek -- an associate of Choi -- should produce much of state-related advertisements. 

Cha is currently being investigated on charges of using his relationship with Choi for illegal gains, such as pressuring another company to give up majority shares of an advertisement company.

An has already testified to the prosecution that he was just following Park’s orders on the fundraising.

Last week, the prosecution found text messages on a phone of another former presidential aide, Jeong Ho-seong, related to Park’s private meeting with the chiefs of seven of Korea’s largest corporations. Park is suspected of pressuring the company heads to donate to the foundations.

The confiscated phone also showed that Park had given specific instructions about Choi, prosecutors said.

According to the investigators, one of the messages showed Park asking if he had received confirmation from Choi. She had referred to Choi as “a teacher,” which in Korean is also used as a term of respect.

A voice recording from Jeong’s phone also showed that Choi gave specific instructions on a variety of reports being sent to Cheong Wa Dae.

Rep. Moon Jae-in, a former leader of the main opposition Democratic Party of Korea, said Wednesday that the prosecution should treat Park as a suspect if she continues to not cooperate with the investigation.

“She was the one who promised (to cooperate). Complying with the investigation is the first step to uncovering the truth. If she were to flip-flop on that, who will believe her resolve to tell the truth?” he said.

By Yoon Min-sik (minsikyoon@heraldcorp.com)