Born in the province of Thừa Thiên, Huế, Sy Dang came from a long line of devout Roman Catholics, including Michael Dinh-Hy Ho, one of the Vietnamese Martyrs.
[citation needed] After his graduation from the Vietnamese National Military Academy in Da Lat and having attended the U.S. Infantry Center & School at Fort Benning, Sy Dang quickly progressed to the rank of major, assigned to the First Infantry Division and was named as deputy Governor and Security Chief, in charge of Thừa Thiên and Huế city.
As Deputy Governor in charge of Huế's security, Major Sy Dang was held responsible for the deaths of nine Buddhists.
[4][5] There are other minority accounts, which suggested Major Đặng was at the right time and place for a set-up by third party with interests in seeing the Diệm regime fall.
Journalists Arthur Dommen and Ellen Hammer speculated that an American serviceman and a handful of CIA operatives orchestrated the entire affair.
[6] Marguerite Higgins and an independent United Nations investigative team reported on May 8, 1963, at 8:00 p.m. that a large crowd, under the leadership of Vietnamese Mahayana Buddhist monk Venerable Thích Trí Quang, besieged Huế radio station to broadcast their request for religious rights.
On the pretext of "defending" against possible "Việt Cộng attack" in darkness, Dang signaled his men, with three shots to the air, to use MK3A2 concussion grenades to subdue the crowd and "secure" the area.
[8] Facing internal unrest and U.S. government disapproval, Khánh commuted Đặng's death sentence to life with hard labour at Côn Sơn with payments to victims' families.