Vehicles, including one carrying President Yoon Suk Yeol, pass a thoroughfare near the presidential residence in central Seoul toward the headquarters of the Corruption Investigation Office for High-ranking Officials in Gwacheon, Gyeonggi Province, Wednesday. Yonhap

After detaining President Yoon Suk Yeol on Wednesday for questioning over his declaration of martial law on Dec. 3, investigators have 48 hours to decide whether to apply for a separate warrant to formally arrest him.

Few doubt that the Corruption Investigation Office for High-Ranking Officials (CIO) will take that step after weeks of struggling to bring him into custody. To keep him in custody for further questioning, the agency will need to file for an arrest warrant by Friday morning.

The anti-corruption agency told reporters that investigators, led by its deputy chief, Lee Jae-seung, began questioning Yoon at 11 a.m.

With over 200 pages of inquiries prepared, investigators are expected to focus on uncovering what motivated Yoon to impose martial law and how deeply he was involved in planning it.

The investigators suspect that he may have committed at least two serious offenses — abuse of power and insurrection — through his actions to authorize and implement the decree.

Other key questions include whether he had a clear intention to incite violence with the goal of "excluding national power from all or part of the territory" of the country, or of "subverting the Constitution" — the legal definition of insurrection, which carries a death penalty. Critics argue that a violent attempt to paralyze the operation of the National Assembly could qualify as such, claiming that Yoon allegedly ordered martial law troops to remove lawmakers from the Assembly to prevent them from voting to lift the decree.

Citing high-ranking officials from the intelligence agency and the military, prosecutors accused Yoon of compiling a list of politicians and other figures critical of him, with the intention of detaining them in an underground bunker near the Capital Defense Command in Seoul.

Supporters of Yoon have defended him, arguing that as president, he had the prerogative to issue the decree and that he lawfully lifted it after the National Assembly voted to reject it.

A photo zone is set up for reporters in front of the headquarters of the Corruption Investigation Office for High-ranking Officials in Gwacheon, Gyeonggi Province, Wednesday, ahead of President Yoon Suk Yeol's arrival for questioning regarding his imposition of martial law. Yonhap

During the interrogation, Yoon mostly remained silent, according to the CIO. He also refused to be recorded on tape, it added.

Speaking to reporters earlier, Yoon's attorneys said he will not cooperate with the CIO as they believe the institution has no legal authority to investigate accusations of insurrection, citing the law which clearly designates only the police to handle such matters. However, the CIO has maintained that it is entitled to investigate the charge as "a related crime."

After the questioning, Yoon was taken to the Seoul Detention Center in Uiwang, Gyeonggi Province, where he was kept in isolation from other inmates.

Typically, if an arrest warrant is approved for a suspect, the person would be required to share a room with other inmates. However, if the warrant is approved for Yoon, he is expected to be allowed to use a solitary room, given that he is still a sitting president.

According to the law on presidential protection, the detention center could be designated as a place of security. In such a case, the detention center staff would be required to check workers, inmates, and visitors to the facility under the direction of the Presidential Security Service.

When an arrest warrant is issued, investigators have 20 days before an indictment. Since the prosecution holds the right to indict a president, the two agencies have agreed that the investigation will be concluded within the first 10 days and the case will then be handed over to prosecutors.

His fate rests in the hands of the eight justices of the Constitutional Court, which is expected to rule on his impeachment case within six months.