Germany's BND agency as early as 1952 had a lead that Eichmann was hiding in Buenos Aires, German newspaper Bild writes, citing recently released intelligence files.
"SS colonel Eichmann is not to be found in Egypt but is residing in Argentina under the fake name Clement," the file, dated 1952 and reproduced in the Bild newspaper, reads. "Eichmann's address is known to the editor of the German newspaper Der Weg in Argentina."
The BND didn't inform the CIA about this lead until 1958, writes Bild, which successfully sued the German government to release the files.
A top Nazi bureaucrat who tried to render the mass killings of Jews as efficient as possible, Eichmann was snatched by Israeli agents in 1960 in Buenos Aires and flown to Israel, where he was tried, convicted of crimes against humanity and hanged in 1962.
The trial created a major media sensation and was broadcast live by several TV and radio stations across the globe. Eichmann's execution remains the only civil one carried out in Israel, which has a general policy of not enforcing the death penalty.
There have long been rumors that West German authorities and the CIA knew about Eichmann's whereabouts well before Eichmann was put on trial in Israel.
Observers say the BND didn't want to release its files related to Eichmann because it fears that they prove that German and Vatican officials assisted Eichmann -- just as they reportedly helped other Nazi war criminals -- in fleeing to Argentina.
By the time the BND informed the CIA about Eichmann, in 1958, the Americans wanted to protect Bonn but were also eager to hide the fact that they themselves had hired former Nazi spies, observers say.
The Mossad team was sent to Argentina after having been tipped off by a Holocaust survivor living in Buenos Aires. The man's daughter had met Eichmann's eldest son and told her father about his anti-Semitic comments.
The American Gathering of Holocaust Survivors and their Descendants said it was "disturbing" that Eichmann's whereabouts may have been known years before he was arrested.
"Equally disturbing is the continued unwillingness of the BND to release the documents which could shed further light on this sad history and other questions related to the fate of Nazis after the war," the group said in a statement. "The question must be asked whether BND files will reveal assistance and aid given to these Nazis to escape and evade justice? History and memory demand the answer to this question."