Lee Chun-jae was born on January 31, 1963, in Hwaseong, Gyeonggi Province, South Korea. His early life was marked by a tragic event when his younger brother drowned during childhood. This incident reportedly had a significant impact on Lee and affected him deeply. According to his mother, he performed well in school and got along nicely with others.

After completing high school in February 1983, Lee joined the Republic of Korea Army. He served as a tank driver and completed his military service in January 1986. Following his discharge, he sought employment and began working for a construction company in 1990. Initially, he worked as an unlicensed crane operator in the Cheongpa-dong area of Yongsan District in Seoul. The next year, he took a position as a crane driver in Cheongwon, North Chungcheong Province. He left this job in March 1993.

In April 1992, Lee married a woman who worked as a bookkeeper. The couple had a son together. However, Lee struggled with alcoholism and often showed violent behavior towards his wife and child.

On September 26, 1989, Lee was involved in a burglary in Suwon. He was caught by the landlord, which led to his arrest. In February 1990, Lee was sentenced to one year and six months in prison for robbery and violence. After appealing the sentence, Lee's punishment was changed to two years' probation, and he was released in April 1990.

Between September 15, 1986, and April 3, 1991, Lee Chun-jae committed a series of brutal murders known as the Hwaseong serial murders in South Korea. The first victim was Lee Wan-im, a 71-year-old woman who disappeared while returning home. Her body was found in a pasture just four days later. The following month, a 25-year-old woman named Park Hyun-sook vanished after getting off a bus. Her body was discovered in a canal three days later.

In December 1986, Kwon Jung-bon, another 25-year-old woman, went missing outside her home. Her body was found four months later in an embankment. Over the next few years, additional murders occurred, each following a similar pattern. Victims were usually young women found bound, gagged, and often strangled with their own clothing.

The final known victim was Gwon Soon-sang, a 69-year-old woman, who was found dead on April 4, 1991, after being raped and strangled. In total, there were ten confirmed victims linked to Lee during this time frame.

The investigation into these murders became the largest in South Korean history, involving over 21,000 suspects and millions of hours of police work. However, the case remained unsolved for three decades.

In 2019, advancements in DNA technology linked Lee Chun-jae to the crimes. He confessed to all ten murders and also admitted to four additional, previously undisclosed murders. Lee was already serving a life sentence for the murder of his sister-in-law at the time of his confession.