Officials say that they have tried to interview Yoon, but he had decided to remain silent and not answer questions.
However, before his arrest, he released a video saying he would cooperate with the investigators, whilst maintaining he felt they were acting illegally.
He can be held until Friday, after which investigators would need to apply for another arrest warrant to keep him in custody – or he will be released, and free to return to the presidential residence.
In a separate development, South Korea’s highest court started a trial to decide on whether to support parliament’s impeachment of Yoon.
Impeachment is the process of bringing charges against an official for wrongdoing in office, and if it passes, President Yoon will lose his job.
Even though President Yoon’s impeachment was approved in Parliament, the Constitutional Court of Korea has the final say.
If it doesn’t agree with the impeachment, then President Yoon can keep his job and stay in office.
But if it approves the impeachment, President Yoon will be removed and an election must be held within 60 days to decide who will get his job.