A Seoul court on Monday denied an extradition request by the United States for a criminal who ran one of the world's biggest child porn sites.

The Seoul High Court said it decided to reject the request from the United States to extradite Son Jong-woo, the operator of Welcome to Video, which ran on the darknet, inaccessible by regular web browsers, because having him here in Korea would be more helpful for the country's fight against child pornography.

"It cannot be ruled out that the extradition (of Son to the US) could hamper South Korea's investigation into sexually exploitative content," the court said, citing that extraditing him would make it harder for Korean authorities, which have been investigating his case, to secure evidence to crack down on illegal content consumers in the country.

"The decision should not be interpreted as exonerating him," the court said, adding that "Son should actively cooperate with the investigation and face proper punishment."

Son's father, who attended the hearing, told reporters that he thanked the court for "the wise decision."

"I feel sorry for the victims," he said. "I don't think it is right to take his side just because he is my son. I will make him accountable for any more sins he has committed."

US authorities have requested the extradition of Son Jong-woo, the operator of Welcome to Video, which ran on the darknet, inaccessible by regular web browsers.

He was indicted by a federal grand jury in the District of Columbia in the United States in August 2018 on nine counts for his operation of the massive child sexual exploitation site.

In the previous two hearings of the extradition case, Son's lawyer demanded South Korea guarantee that he won't be punished in the US for producing and distributing child pornography, citing Korea's extradition laws that rule against double punishment for the same criminal activity.

During the second trial on June 16, Son made an appeal in a court appearance to go through legal processes in South Korea, where punishments for crimes related to child pornography tend to be much more lenient than in the US.

Son was arrested in Korea in March 2018 and convicted of generating and distributing exploitative content for fees paid using the cryptocurrency Bitcoin.

During the arrest process, authorities found approximately eight terabytes of child sexual assault videos.

He finished serving an 18-month prison term in April but was taken back into custody since an arrest warrant was issued for potential US extradition.

Son operated the site from June 2015 until March 2018, when it was taken down by law enforcement.

Officials around the world worked together to chase down the site's users and arrested 337 people, including 223 Koreans. At least 23 underage victims abused by the site's users were rescued.

In early May, Son's father filed a complaint against his son for what he argued was a violation of laws that prohibit proceeds from criminal activities from being concealed. The move was widely seen as a bid to stop the extradition by having him face a legal process in Korea.

With the court's decision Monday, Son is expected to be released from the Seoul Detention Center soon and will be investigated again in connection with the complaint filed by his father, along with international money laundering charges. (Yonhap)