That's not exactly correct. Under the US-ROK SOFA, SOFA members who violate ROK law in areas under ROK jurisdiction (i.e. off post) are subject to ROK prosecution. At least as far back as the 90s when I commanded an MP company in Korea, there was a special wing at Cheonan Prison specifically for SOFA members who had received sentences in ROK courts under ROK law. There were provisions for them to receive regular visits/inspections by US military authorities, but they were, to be sure, prisoners of the ROK correctional system.
The SOFA does give the ROKs some latitude. If two GIs get in a brawl in downtown Itaewon, then it's likely they'd be turned over to the US military, but if they busted out the window of a Korean storefront or beat the snot out of a Korean shopkeeper, chances are they're going to face charges, trial and potential incarceration under the Korean system.
Thanks, understand. I know the SOFAs have been changed over the years. I’m “ancient vintage,” having grown up an Army brat and then 24 years in the Navy many moons ago. There was a time when U.S. servicemen were handed over to U.S. authorities, regardless of the circumstances. When my father was a military attaché in a certain European country, he dealt with the case of a soldier who had killed a local. A significant incident to be sure, but it was handled discreetly between the two countries. The soldier was released to U.S. custody, taken out of the host country, and punished severely in the U.S. As legal officer in my first fleet squadron (a collateral duty), I frequently had to deal with situations of sailors getting into trouble ashore during port visits. If we had a SOFA with the country we were visiting, most often the sailor or Marine was turned over to the ship. Admittedly, if we didn’t have a SOFA, it became difficult to retrieve the individual(s). A different time when the United States was more respected and even feared; foreign governments did not mess with the U.S. government or its citizens, law abiding or law breaking.
This was my understanding as well (2012-15). PV2 Knucklehead’s whole world gonna change now... I can’t imagine why his unit wasn’t tasked to escort him to Bliss.