South Korea's ousted premier said on Thursday that he had opposed suspended President Yoon Suk Yeol's declaration of martial law, testifying for the first time at his former boss's impeachment trial about the events of a night that threw the country into turmoil.

South Korean President Yoon Suk Yeol contested his arrest on rebellion charges in one court and pleaded to preserve his presidency in the other, both cases related to his brief imposition of martial law.

Yoon denies ordering arrest of key politicians and accuses former first deputy director of South Korea’s spy agency of lying and fabricating evidence

South Korean police are formally building a case against impeached President Yoon Suk Yeol over accusations he obstructed the execution of an arrest warrant, a police spokesperson said on Friday. A South Korean court issued an arrest warrant for Yoon on December 31 in a criminal investigation accusing the suspended leader of insurrection over his martial law decree last year.

Impeached South Korean President Yoon Suk-yeol appeared before two courts on Thursday. His first stop at the Seoul Central District Court made him the first sitting president — he’s not yet been formally removed from office — to face criminal prosecution.