Ko Wen-je, former leader of Taiwan’s opposition party, was arrested after almost 19 hours of interrogation in connection with a property development scandal that occurred while he was mayor of Taipei.

Ko was taken into custody late Friday night due to concerns about possible collusion, after he refused to continue overnight questioning, according to a report by the Central News Agency that cited the Taipei District Prosecutor’s Office.

Under Taiwan’s laws, prosecutors must request a court to detain a suspect or witness within 24 hours of interrogation. Ko has requested a judicial review of the arrest decision, the CNA report said.

Ko, a former trauma surgeon and surprisingly popular third-party candidate in the latest Taiwan’s presidential race, garnered almost 27% of the vote in January. He finished behind the eventual winner, President Lai Ching-te, and runner-up Hou Yu-ih of the Kuomintang.

The incident involving Ko is the latest in a series of investigations into Taiwanese politicians for corruption or misconduct since President Lai took office in May this year. In July, former vice premier Cheng Wen-tsan of the ruling Democratic Progressive Party was detained on corruption charges.

Ko announced on Thursday that he would temporarily step down as chairman of the Taiwan People’s Party amid a series of scandals related to the party’s expenses, including the use of election subsidies and political donations.

The TPP in a statement on Saturday urged the court to consider the justifiability of the arrest.