A declassified record from the Korean War shows an American colonel telling his South Korean counterpart it "would be permitted" to machine-gun 3,500 political prisoners, to keep them from joining approaching enemy forces.

Other American officers observed, photographed and confidentially reported wholesale executions by their South Korean ally in 1950. The secretive slaughter is believed to have killed 100,000 or more leftists and supposed sympathizers, usually without charge or trial in a period of just a few weeks.

Extensive archival research by The Associated Press has found no indication that Far East commander General Douglas MacArthur took action to stem the summary mass killing.

Knowledge of the killings reached top levels of the Pentagon and State Department, where it was classified "secret" and filed away.

Now, more than a half-century later, the South Korean government's Truth and Reconciliation Commission is investigating what happened in that summer of terror.

A debate continues over how to distribute the blame.