Let it go. Whoever did it was acting on behalf of their government, not as a criminal, in an undeclared war. That war is over. So, under the Supreme Court’s new doctrine, the combatants in that war, unlawful though they may be, are entitled to be treated as POWs. Even if you found out who it was, you have to release them at the end of the war.
You are assuming that that particular war is over.