Yoon Suk Yeol, the impeached South Korean president who is standing trial on insurrection charges over his decision to impose martial law in December, was released from a detention center on Saturday, a day after a court ruled that his detention was invalid.
The Seoul Central District Court ruled on Friday that prosecutors had violated procedural rules by holding Mr. Yoon in detention longer than legally allowed before indicting him in January. The procedural violation rendered Mr. Yoon’s detention invalid, the court said.
Prosecutors, who had a week to appeal the decision, requested instead that he be released.
Mr. Yoon smiled broadly and waved at supporters as he walked out of a detention center south of Seoul, where he had been held since Jan. 15. He clenched his fist in a victorious gesture and bowed toward hundreds of supporters who had gathered outside the jail, waving national flags and shouting, “Yoon Suk Yeol!”
His release does not affect the insurrection charge he faces in a Seoul criminal court related to his martial law declaration, or the separate proceedings at the Constitutional Court. That body is deliberating whether his parliamentary impeachment was legitimate, and if he should be formally removed from office. But it does mean that he will be free while standing trial.
After a short ride from the detention center, Mr. Yoon returned to his presidential residence on a hilltop in central Seoul. As a motorcade carrying Mr. Yoon neared his residence, thousands of supporters lined the street to cheer him. Mr. Yoon briefly got out of his car to shake hands with the supporters, who called his impeachment and the insurrection charge against him a “fraud” engineered by his political enemies.
Mr. Yoon sounded as defiant as ever, calling his legal struggle “a fight to defend the freedom and rule of law in South Korea” and “a resolute standoff against those who want to usurp power by illegal means.”
“I will persist in this fight to the end together with the people,” Mr. Yoon said in a statement.
His release was the latest twist in the political upheaval and uncertainty that was unleashed when he declared martial law on Dec. 3, calling the opposition-controlled National Assembly a “monster” that “paralyzed” his government.
His abrupt imposition of martial law triggered a national outrage, prompting thousands of people to rush to block military troops from taking over the Assembly. That gave time for lawmakers to vote down his decree. His martial law ended in six hours.
Mr. Yoon’s party blocked the Assembly’s first attempt to impeach him on charges of disrupting constitutional orders. But it impeached him in its second attempt on Dec. 14, suspending him from office until the Constitutional Court delivers its final say on his political fate.
Separately, prosecutors went after him with insurrection and other criminal charges. Their first attempt to detain him, on Jan. 3, was aborted when he was holed up in his residence, surrounded by his bodyguards, and refused to hand himself over. He surrendered only when prosecutors visited again on Jan. 15 with more police officers.
He is the first president in South Korean history to be detained on criminal charges while still in office.
His lawmakers have since tried to release him, disputing his impeachment, his arrest and the criminal charges against him.
In the end, Mr. Yoon was released from jail because of a procedural error that prosecutors made about how long the warrant they used to detain him was valid. By law, if prosecutors fail to indict a criminal suspect before such a warrant expires, the suspect must be released from custody.
Prosecutors, who believed that the warrant on Mr. Yoon would expire at 7:39 p.m. on Jan. 26, indicted him about an hour before that. But in its ruling on Friday, a three-judge panel at the Seoul Central District Court said the warrant had expired on the morning of Jan. 26.
The court ruling did not address any criminal charge Mr. Yoon faced. But his release is expected to encourage his supporters. His critics also feared that he would try to rally their support with his increasingly polarizing language to divide the country and build pressure on judges deliberating his case.
Prosecutors said on Saturday that they had decided not to appeal the court’s decision because they were not likely to win. But they vowed to win the main criminal trial against Mr. Yoon.
The Democratic Party, the country’s main opposition, accused prosecutors of turning their “back on the people.” It also denounced Mr. Yoon’s behavior after his release as “appalling.”
“He continues to defy the reality of his situation — that he remains a criminal suspect facing charges related to treason,” said Yum Seungyul, a party spokesman. “His actions today serve only to further divide and destabilize a country already on the edge.”
Mr. Yoon’s surprise release could deepen and potentially prolong South Korea’s political crisis, said Leif-Eric Easley, a professor of international studies at Ewha Womans University in Seoul.
“The Constitutional Court is already under political pressure from pro- and anti-impeachment protesters in the streets,” he said. “Yoon’s release from detention will energize his supporters and raise further doubts about the legal process against him.”