On May 6, 1948 the decision was made to replace Lieutenant Colonel Kim Ikryeol (김익렬, commander of the 9th Regiment of the Korea Constabulary) with Lieutenant Colonel Park Jingyeong (박진경). With the newly shuffled 11th Regiment (essentially an expanded and renamed 9th regiment), Park Jingyeong was given the task of suppressing the uprising in Jeju. USAMGIK viewed Park Jingyeong's work in high regard and he was quickly promoted to the rank of Colonel for his work in the suppression operation.

USAMGIK received a shock when news came that Park Jingyeong had been assassinated in the barracks on the morning of June 18, 1948. The assassination did not go down well with USAMGIK who had all rated Park Jingyeong very highly. A thorough investigation was done. Eight people were arrested. The two most notable of the arrested were First Lieutenant Moon Sanggil (문상길) and Staff Sergeant Son Seonho (손선호). Moon Sanggil was the reported leader of the group who had planned the assassination and Son Seonho was the one who actually shot and killed Park Jingyeong.

At the court martial trial (which was held in Seoul) Moon Sanggil was accused of planning the assassination at the order of Kim Dalsam (김달삼), who was the overall commander of the armed resistance group. However, he denied this charge and stated that he planned the assassination because he agreed with former commander Kim Ikryeol and did not want to participate in a fratricidal war against the Jeju people. Son Seonho (from the 5th Regiment from Busan) and the other soldiers stated they participated in order to stop what they considered to be a ruthless repression operation and they wanted to save the country from being destroyed by a fratricidal war. Park Jingyeong had reportedly said it was necessary to 'sacrifice' the lives of Jeju citizens in order to suppress the fighting.

In the end both were sentenced to the death penalty. Moon Sanggil and Son Seonho were executed by firing squad on September 23, 1948. Before being executed both prayed that the South Korean Army would serve only the South Korean people and not just for the powerful.

References

The National Committee for Investigation of the Truth about the Jeju April 3 Incident - "The Jeju 4.3 Incident Investigation Report" (downloadable here in English)