The Office of Special Investigations (OSI) of the U.S Justice Department was created in 1979 to identify and expel, from the United States, those who assisted Nazis in persecuting "any person because of race, religion, national origin, or political opinion." This involved gathering, verifying, and presenting in court eyewitness and documentary evidence of decades-old crimes. The evidence was incomplete and scattered around the world. Much of it was then in Eastern Europe, behind the Iron Curtain. Nonetheless, the OSI investigated 1,700 persons suspected of being involved in Nazi war crimes. Over 300 have been prosecuted with at least 100 stripped of their U.S. citizenship and 70 deported, the most recent in 2021. Others have left voluntarily, fled, or have been blocked from entering the U.S.

Immediately after World War II, Americans chose not to dwell upon the war's atrocities, and cold war threats caused governments to recruit former Nazis for intelligence work. Newly formulated U.S. immigration policies and prejudice created obstacles for entering the United States by people displaced by the war. As a result, it became easier for former Nazis and their collaborators to enter the U.S. than for Holocaust survivors. Sometimes protected by U.S. Intelligence officials, war criminals found a safe haven in America. OSI was founded to ferret them out. It operated as a separate unit until 2010 when it was merged with the Domestic Security Section of the Justice Department Criminal Division to form a new unit, the Human Rights and Special Prosecutions Section (HRSP). According to The Washington Post, the United States has successfully prosecuted more Nazis than all other countries combined and is "widely deemed to have the world's most aggressive and effective Nazi-hunting operation" While efforts continue to prosecute those involved in atrocities during World War II, the principal focus of HRSP's human rights enforcement work is now on prosecuting war criminals from postwar conflicts including those in Bosnia, Serbia, Rwanda, and Guatemala.

A thorough history of OSI was produced by legal historian Judith Feigin of the Justice department in 2006. It concluded that, in addition to having obtained some measure of justice for wartime atrocities, OSI set international standards for prosecuting perpetrators of genocide and made substantial contributions to the historical record that "stand as a permanent and irrefutable response to those who would deny the Holocaust and its horrors." Further, "the message resonating from OSI’s cases is that the United States does not choose to add to its populace persons whose actions victimized innocent civilians."