Quoting Max Hastings’s The Korean War, page 38:

The 12,000 Japanese in their ranks were sent home. But the 8,000 Koreans who remained—the loyal servants of a brutal tyranny in which torture and judicial murder had been basic instruments of government—found themselves promoted to fill the higher ranks, while total police strength in South Korea doubled. […] A long roll call of prominent torturers and anti‐Nationalist fighters under the colonial power found themselves in positions of unprecedented authority. In 1948, 53 percent of officers and 25 percent of rank‐and‐file police were [Imperial] Japanese‐trained. By a supreme irony, when the development began of a Constabulary force, from which the South Korean Army would grow, the Americans specifically excluded any recruit who had been imprisoned by the [Imperialists]—and thus any member of the anti‐[Imperial] resistance.

(Emphasis added.)

Likewise, Jeremy Kuzmarov notes in Modernizing Repression, pg. 81:

The [American Military Government of South Korea] retained 80 percent of pro‐[Imperial] officers above the rank of patrolman, including northern exiles experienced in suppressing the anticolonial underground. As Colonel William Maglin, the first director of the KNP, commented, “We felt that if the Korean element of the KNP did a good job for the Japanese, they would do a good job for us.” A June 1947 survey determined that eight of ten provincial police chiefs and 60 percent of the lower‐ranking lieutenants were [Imperialist]‐trained, a crucial factor triggering opposition to the police.

Raise your hand if you notice anything familiar.