Those mass graves, long spoken of as “fiction” or leftist propaganda or else blamed on the North Korean army by US and South Korean officials, are still being uncovered today as the Korean Truth and Reconciliation Commission attempts to fulfill its brief.
The victims were supposed to be Communists working with the North Koreans, but according to a former prison guard/executioner who testified before the Truth and Reconciliation Commission, they were really garden variety criminals, peasants rounded up in random sweeps, even women and children. The History Blog
Also see US Archives and "Did Americans Mass-Murder Korean Women and Kids?" with lots of links
Picasso's famous painting of Korean women and children being butchered by white men (1951) Musée Picasso, Paris