Mr. Tan is claiming that President Lee was part of a gang rape and murder of a woman as a juvenile. I find this very hard to believe considering how long he has been in the public spotlight. Evidence of something like this occuring would have definitely leaked out by now:

Police have opened an investigation into a Korean American professor for possible defamation charges after he allegedly made damaging comments about President Lee Jae Myung with false information, officials said Tuesday.

The investigation against Morse Tan, dean of Liberty University School of Law, came after a conservative civic group had filed a complaint with the police, accusing Tan of defaming Lee by spreading false information about him.

In June, Tan said during an event in Washington that Lee had been involved in the gang rape and murder of a girl during his youth, and that he was sent to a juvenile detention center and unable to finish middle and high school.

The civic group said these claims are unfounded.

Tan, former U.S. ambassador-at-large for global criminal justice under the first Donald Trump administration, is known for promoting conspiracy theories about election fraud in South Korea.

According to the civic group that filed the complaint, Tan also claimed that the June 3 snap election won by Lee was rigged.

Yonhap

You can read more at the link, but with Tan currently in Korea it will be interesting if the ROK government tries to detain him or just let him go back to the U.S. and deny future entry.