June may mark the 55th anniversary of the end of the Korean War, but only in recent years has the ugly truth of that tragic civil conflict begun to be uncovered in the form of mass graves, declassified documents and personal confessions.

According to a recent Associated Press story, the South Korean government’s two-year-old Truth and Reconciliation Commission has unearthed hundreds of sets of remains of Koreans who they believe were mass executed by the nation’s U.S.-backed regime, under then-President Syngman Rhee’s orders, in the summer of 1950. The southern army and police would line up detainees who were suspected leftists or just illiterate peasants, shoot them and dump their bodies into trenches, according to the AP report. Many were never formerly charged nor had trials.

The executions, which occurred over weeks as North Korean forces pressed south, were largely hidden from history for half a century, said the report, but now with the work of a government-sanctioned commission, charges long made by victims’ family members, historians and journalists are being legitimized.

They were “the most tragic and brutal chapter of the Korean War,” historian Kim Dong-choon, a commission member, told the AP.

The commission estimates 100,000 people were executed in a South Korean population of 20 million, according to the news report, though the actual number could be more than double that. The commission has officially confirmed two large-scale executions in the South Korean county of Cheongwon and at Ulsan on the southeast coast. It is also investigating accusations of the U.S. military indiscriminately killing civilians, mostly in air attacks, the AP reported.

South Korean conservatives complain that such investigations will only reopen wounds from a period that saw people at the village level carrying out individual executions, based on suspected leftist or rightist leanings. But the Commission’s Kim told the AP that by exposing the truth of war, it hopes to heal the “pain of the bereaved families,” and to prevent future wars.