South Korea’s anti-corruption agency will resume questioning President Yoon Suk Yeol on Thursday as part of a criminal probe into whether he committed insurrection, while the Constitutional Court holds a second hearing of the embattled leader’s impeachment trial.

South Korea is grappling with its worst political crisis in decades, sparked by Yoon’s brief attempt to impose martial law on Dec. 3 that was voted down by parliament.

On Wednesday, Yoon became the first incumbent president to be arrested in South Korea, ending a weeks-long standoff with authorities after police swooped before dawn on his fortified hillside villa in Seoul to the despair of followers at the site.

Yoon said he turned himself in for questioning by corruption investigation officials to prevent what he called the risk of “unsavoury bloodshed”, though he continued to protest that it was an illegal investigation and invalid arrest warrant.

Authorities have 48 hours to question the suspended president, after which they must seek a warrant to detain him for up to 20 days or release him.

Yoon has up to now refused to talk with investigators who had prepared a questionnaire of more than 200 pages, an official from the Corruption Investigation Office for High-ranking Officials (CIO) that is heading the criminal inquiry said on Wednesday.

His lawyers have said the arrest warrant is illegal because it was issued by a court in the wrong jurisdiction and the team set up to investigate him had no legal mandate to do so.

After apparently stonewalling investigators, Yoon was taken on Wednesday evening to the Seoul Detention Centre, where he is expected to have spent the night in a solitary cell.

His questioning is due to resume at 2 p.m. (0500 GMT) on Thursday afternoon, Yonhap News Agency reported.

Separate from the criminal investigation, the Constitutional Court will hold a second hearing on Thursday of Yoon’s impeachment trial.

Parliament impeached Yoon on Dec. 14, suspending his powers and the court is now deliberating whether to permanently remove him from office or restore his presidential powers.

Opinion polls show a majority of South Koreans support impeaching Yoon, but the attempts to arrest him appear to have rallied his hardcore supporters.