Sometimes the revenge killings were fueled not just by political ideology, but also by prewar family feuds. Villagers often wiped out entire families so that there would be no one left to retaliate.

After the war ended, those murdered by the Communist invaders and leftist vigilantes were treated like martyrs in South Korea.

But military dictators who ruled South Korea after the war banned any public discussion of the atrocities committed by the South Korean police and right-wing vigilantes. The police put the victims’ families under surveillance and kept secret files on them into the 1980s. The families themselves hid their backgrounds, fearful of the stigma of being labeled the “reds’ offspring.”

Today, many victims remain buried where they were executed and dumped nearly seven decades ago.

“There is still a leftist-rightist tension at the bottom of our society, with the red stigma not yet removed and many people deeply uncomfortable with any attempt to excavate the past,” Mr. Park said. “One way of healing the wounds that still divide our society is to recover the remains and return them to their families.”

Mr. Park, a Seoul native, was a history major and aspiring journalist at Yonsei University in Seoul when he fell in love with archaeology while interning in a museum. But he had little inkling that he would become involved with Korean War remains when he returned home in 1989 with a doctorate in human osteology from the University of California at Berkeley and began teaching at Chungbuk National University.