Baek Dong-heum, a senior police officer at the National Office of Investigation, speaks during a press briefing at the National Police Agency in central Seoul, Monday. Yonhap

The national anti-corruption agency is facing intense criticism for its mishandling of a crucial investigation into President Yoon Suk Yeol's declaration of martial law late last year, which was quickly thwarted by lawmakers.

The Corruption Investigation Office for High-ranking Officials (CIO) has been accused of poor coordination with the police during their joint probe. The situation worsened, Monday, when the CIO initially decided to transfer the responsibility of enforcing a detention warrant for the president to the police, only to reverse the decision shortly after.

This misstep has raised concerns that the investigation will face further setbacks, particularly since the president has refused to comply with the detention warrant issued on charges of insurrection and abuse of power. The CIO, working with the National Office of Investigation (NOI) and an investigative unit from the defense ministry, had hoped to rely on the police's expertise to execute the warrant, but this decision only strengthened Yoon's supporters.

Around 40 lawmakers from the ruling People Power Party (PPP) gathered near the presidential residence in central Seoul to rally against attempts by investigators to detain Yoon.

In response to the backlash, the CIO eventually abandoned its plan to entrust the execution of the warrant to the police.

"Given the seriousness of the case, there should be no room for controversy in the investigation. We will take the lead in the investigation within the joint investigation unit," a CIO official said.

Last Friday, the CIO attempted to detain Yoon but withdrew its investigators after being blocked by the Presidential Security Service (PSS). Lee Jae-seung, the deputy CIO chief, said that the agency did not anticipate such strong resistance from the PSS.

Regarding the investigation's authority, Lee said, "The police agreed on the CIO's leadership in the investigation because we have legal expertise and the right to seek an arrest warrant. Based on the progress of the probe, if our work is finished, the case will be forwarded to the prosecution, which holds the authority to indict. If a special counsel investigation is confirmed, it will be handed over to the counsel."

The CIO said it refiled the detention warrant at the Seoul Western District Court to extend the deadline, which was set to expire at midnight on Monday, but did not provide further details.

Around 40 ruling People Power Party lawmakers gather near the presidential residence in Seoul, Monday, to rally against attempts by investigators to detain President Yoon Suk Yeol. Yonhap

The agency's move prompted criticism from both the police and Yoon's legal team.

The police said the request to take over the execution of the warrant was made unilaterally by the CIO, adding that the move lacks legal basis.

"After conducting an internal review, we determined that the anti-corruption agency's request is legally controversial," Baek Dong-heum, a senior police officer at ther NOI, said at a press briefing. "We will continue to consult with the CIO regarding the execution of the warrant."

Police also warned that they will consider arresting the presidential security officials who obstruct the execution of the warrant again.

Yoon's lawyer, Yun Gap-keun, condemned the decision, likening it to subcontracting in a construction project.

"Watching the CIO's investigative behavior that lacks legal ground raises doubts about its qualifications and abilities as a state agency," Yun said in a statement.

Yoon's legal team filed a complaint with the prosecution, Monday, seeking an investigation into 11 law enforcement officials, including CIO chief Oh Dong-woon. They claimed that the anti-corruption agency does not have the authority to direct the police's investigation, yet it attempted to direct police officers when executing the detention warrant.

The CIO's move also drew criticism from the PPP.

"This clearly reveals that the CIO lacks expertise and responsibility, let alone the ability to investigate the president," Rep. Shin Dong-wook, a spokesperson for the PPP, said. "The behavior of neglecting its duty as a state agency damages the rule of law and constitutional order that can never be tolerated."

In addition to the criminal investigation, Yoon is also facing an impeachment trial at the Constitutional Court on charges of insurrection and abuse of power.