Once the invasions were underway, all American prisons in the newly-invaded lands were emptied of prisoners incarcerated under the American justice system.
This was a propoganda move in order to send the message that America ran itself deep into debt because they incarcerated more prisoners than necessary.
Moreover, all prisoners were freed under the condition that they serve the Greater Korean Republic.
Zacarias Moussaoui, the "20th hijacker" of the 9/11 attacks, was incarcerated at a supermax facility in Florence, Colorado but released when the Greater Korean Republic offered for him to become a commando for the Korean People's Army.
In California, the more dangerous and uncontrollable prisoners were executed as to clear the prisons for people likely to rise up against the Occupation.