A South Korean court on Thursday overturned the murder conviction of a man who had already served 20 years of a life sentence he received 31 years ago.

The Suwon District Court, in acquitting Yun Sung-yeo of the 1988 rape and murder of a 13-year-old girl, said it found the confession from Lee Chun-jae, a jailed killer, to be credible.

Appearing as a witness at Yun’s retrial hearing last month, Lee said he, not Yun, had killed the girl.

He also admitted to killing 14 girls and women and raping nine others three decades ago, in one of the most notorious unsolved serial murder cases in the country. Yun was the only person ever convicted of any of the crimes.

In a rare gesture, the court apologized for the past failure. “As a member of court, the final bastion of the judicial branch, I apologize,” said one of the judges.

Yun’s lawyers said they would file a civil suit against the country over the wrongful conviction, seeking to expose possible wrongdoing by the police, the forensic service and the prosecution.

“It is certainly fortunate that today Mr. Yun was exonerated of the rape and murder after 31 years. But it is also deeply regretful that those involved in the investigations and the trials that led to the false conviction will not be facing any responsibility,” they said a statement released the same day.

Yun sought a retrial in November last year after new DNA evidence connected Lee to some of the murders.

Lee has been in prison since 1994 for the rape and murder of his sister-in-law. He will not face added punishment for the crimes he confessed to, as the statute of limitations has expired.

By Kim Arin (arin@heraldcorp.com)