There is almost definitely a mechanism if he goes via the Hague, however given the American Service Members Protection Act, which allows the US to unilaterally

There is almost definitely a mechanism if he goes via the Hague, however given the American Service Members Protection Act, which allows the US to unilaterally invade Holland (no, really) should any US soldiers end up in court there, there is little chance of that. Although as far as I am aware, the Hague has ultimately very few legal powers anyway unless the US refuses point-blank to investigate or voluntarily hands over the investigation to them.