The police are investigating whether President Yoon Suk Yeol tried to lead an insurrection when he declared martial law and plunged the country into crisis.

A South Korean court gave authorities approval on Tuesday to detain impeached President Yoon Suk Yeol in a criminal investigation into his martial law decree, marking the first time that a sitting president of the country has faced arrest.

Yoon Suk Yeol, South Korea’s since-impeached president, had been planning for months to impose martial law and target political opponents, according to accounts.