The Office of Special Investigations is a division of the United States Department of Justice which handles war crimes investigations of persons in the United States, not to be confused with the US Air Force criminal investigation division.
For many years OSI had pursued deportation proceedings against Stefan Anders, an ex-German soldier believed to have brutally killed several prisoners during World War II at a concentration camp. Their chief witness against Anders was Leah Glaser, who claimed that she saw him carry out such activities.
Aside from that, however, OSI had difficulty gathering evidence against Anders due to the simple fact the alleged activities occurred so long ago. The investigation was able to move forward slightly when in the early 1990s the Russians opened up their archives of war materials, and OSI was able to link one record to Anders, with the help of Glaser.
It was not until Anders was suspected in Glaser's death that OSI was able to gather evidence from Anders' apartment. It was believed by all sides that this evidence would be sufficient to force his deportation. (L&O: Evil Breeds)