It describes the government’s posthumous pursuit of Dr. Josef Mengele, the so-called Angel of Death at Auschwitz, part of whose scalp was kept in a Justice Department official’s drawer; the vigilante killing of a former Waffen SS soldier in New Jersey; and the government’s mistaken identification of the Treblinka concentration camp guard known as Ivan the Terrible.

So too are references to macabre but little-known bits of history, including how a director of the O.S.I. kept a piece of scalp that was thought to belong to Dr. Mengele in his desk in hopes that it would help establish whether he was dead.

The Justice Department said the report, the product of six years of work, was never formally completed and did not represent its official findings. It cited “numerous factual errors and omissions,” but declined to say what they were.

The Justice Department itself sometimes concealed what American officials knew about Nazis in this country, the report found.

The report also examines the case of Arthur L. Rudolph, a Nazi scientist who ran the Mittelwerk munitions factory. He was brought to the United States in 1945 for his rocket-making expertise under Operation Paperclip, an American program that recruited scientists who had worked in Nazi Germany. (Rudolph has been honored by NASA and is credited as the father of the Saturn V rocket.)

The report cites a 1949 memo from the Justice Department’s No. 2 official urging immigration officers to let Rudolph back in the country after a stay in Mexico, saying that a failure to do so “would be to the detriment of the national interest.”

Justice Department investigators later found evidence that Rudolph was much more actively involved in exploiting slave laborers at Mittelwerk than he or American intelligence officials had acknowledged, the report says.

In chronicling the cases of Nazis who were aided by American intelligence officials, the report cites help that C.I.A. officials provided in 1954 to Otto Von Bolschwing, an associate of Adolf Eichmann who had helped develop the initial plans “to purge Germany of the Jews” and who later worked for the C.I.A. in the United States.

In a chain of memos, C.I.A. officials debated what to do if Von Bolschwing were confronted about his past — whether to deny any Nazi affiliation or “explain it away on the basis of extenuating circumstances,” the report said.