On January 14, 2004, in Bucheon, Gyeonggi Province, he kidnapped, raped and then murdered two people.
[1] He murdered mainly in the southern part of Seoul, including Shin-gil, Guro and Gwanak.
His reason for killing a male elementary school student after sexually assaulting him was that he himself was abused by a man as a child.
On April 12, 2007, he was sentenced to death by the Supreme Court and detained in Seoul Detention Center.
On the morning of November 21, 2009, a jail employee discovered Jeong had attempted to hang himself from a noose made from a plastic bag.