Robert Leiber, S.J. (10 April 1887 – 18 February 1967) was a close advisor to Pope Pius XII, a Jesuit priest from Germany, and Professor for Church History at the Gregorian University in Rome from 1930 to 1960. Leiber was, according to Pius' biographer Susan Zuccotti, "throughout his entire papacy his private secretary and closest advisor". 
Before 1924, Leiber worked with Ludwig Pastor on the publication of his 20-volume Papal History. From 1924–29, he was advisor to Eugenio Pacelli while he was Nuncio in Munich and in Berlin. While Professor at the Gregorian, he continued advising Pacelli, who was then Cardinal Secretary of State. After Pacelli was elected to the papacy as Pope Pius XII in 1939, Leiber helped and advised him until the Pope's death on 9 October 1958. Leiber is described as Pie XII's "most trusted aide". However he never was a Vatican official. He was a respected and feared "unofficial official". According to Mark Riebling, known in papal Rome as the "little asthmatic", "some described him with a Latin quip: Timeo non Petrum sed secretarium eius - "I do not fear Peter [the Pope], but his secretary".
He assisted Pius XII in researching the topics for his speeches and radio messages. Leiber was one of an "impromptu band of willing Jesuits" whom Pius XII employed "checking and double-checking every reference" in his written works. Leiber, stationed at the Pontifical Gregorian University, three miles from the Vatican, complained after Pius XII's death that he was often expected to "drop whatever he was doing and hasten to the Vatican", taking public transportation.
As the Pope's trusted Private Secretary, Leiber acted at the intermediary between Pius XII and the German Resistance. He met with Joseph Muller, who visited Rome in 1939 and 1940 to obtain assistance from the Pope in acting as an intermediary between the Resistance and the Allies in the lead up to a planned coup against Hitler. Later in the war, Leiber remained the point of contact for communications from Colonel-General Ludwig Beck in the lead up to the 1944 July Plot.
After World War II, Pius XII charged Leiber and Bea with investigating the activities of Gertrud Luckner (later declared Righteous among the Nations), the pioneer of a German Catholic philo-Semitic and pro-Israel movement. The Holy Office in 1948 issued a monitum (or warning) to the group, due to concerns that the group's pro-Zionist activities were "encouraging religious indifferentism (the belief that one religion is as good as the next)". Leiber concluded in April 1950 there was nothing theologically wrong with the work of Luckner; Bea went further, actually affirming it.
In an October 1958 meeting, Leiber turned down a position offered by new Pope John XXIII in light of his health, suggesting Augustin Bea instead. He authored several books and articles on Church history and on the Reichskonkordat. After suffering acute asthma attacks for many years, Leiber died in Rome in 1967, aged 79.
According to Phayer, Leiber "sparked new life into Austrian bishop Alois Hudal's plan" to set up a "ratline" — an escape route from Europe for Nazis and fascists, including war criminals. Leiber wrote to Hudal around the time of Operation Barbarossa, telling the latter to "look at the [ratline] mission as a crusade".
According to a history professor at the Pontifical Gregorian University, Leiber had no direct authority to correspond with Hudal but "[his] role as one of Pius XII's closest confidantes allowed the German Jesuit to act as the pope's intermediary and messenger." Hudal maintained contact with Leiber and other Vatican officials during and after the war. Leiber destroyed all his personal papers before his death, rather than leave them for posterity, confirming to van Room that he had destroyed his papers because he feared they "would cast Pius in an unfavorable light". Leiber was in the confidence of German ambassador to the Vatican, Ernst von Weizsäcker (who was later tried at Nuremberg), who informed Leiber that the priest-assistant Cesare Orsenigo, Apostolic Nuncio to Germany from 1930 to 1945, was a member of the Nazi party.
Statements on Pius XII and the Holocaust
After the war, Leiber became actively involved in debates over the legacy of Pius XII during the Holocaust, frequently writing and speaking publicly, always as a staunch defender of Pius XII. Leiber wrote an article, published on 27 March 1963 in the Frankfurter Allgemeine Zeitung, the main claim of which was that Pius XII had limited and generally unreliable information about the Holocaust.
As Lieber related to Dutch historian Ger van Roon, Leiber believed that Pius XII chose not to speak out about the Holocaust because he "wanted to play the peacemaker during the war" by maintaining Vatican neutrality and independence. On this point, Leiber and British diplomat Francis d'Arcy Osborne, another contemporary close to Pius XII, were in agreement. During the war, Pius XII's surrounded himself with German advisers including Leiber, but also Ludwig Kaas and Pasqualina Lehnert. This attracted the attention of United States Department of State historian George Kent and others, who questioned the pope's neutrality given this apparent Germanophilia.
In 1961, Leiber asserted that Pius personally ordered superiors of church properties to open their doors to Jews. As exhaustive studies of Susan Zuccotti and others have shown, no written evidence of this has yet emerged. Historians such as Phayer argue that Catholic institutions in Italy and elsewhere that did admit or help Jews did so "independently, without the Vatican's instructions". For his statistics on the number of Jews he claimed Pius XII to have saved, Leiber relied on fellow Jesuit Beato Ambord; the original compilation of the numbers is unknown.
A more recent study by Dwork and Pelt concurs with Zuccotti, concluding: "Sam Waagenaar challenged Leiber. On the basis of our research, we find Waagenaar's refutation convincing. Pope Pius XII did nothing. Many convents and monasteries helped—but not to the extent that Pius's close associate Robert Leiber claimed." These kind of statements like Zuccotti's ones come from anti-Catholic biases and sound quite absurd: due to the sensitiveness of the matter, the Pope could not send a written order. Had the German occupation troops intercepted it, Hitler could have used it as a pretext in order to invade the Vatican City, arrest the Pope and disband the Catholic Church (and arrest all the hidden Jews).
Above all, Leiber denied that the disbanding of the German Catholic Centre Party had been a quid pro quo for the signing of the Reichskonkordat. Leiber wrote in 1958 that "[Pacelli] wished that [the party] could have postponed its dissolution until after the signing of the concordat. The mere fact of its existence, he said, might have been of use at the negotiating state".
- Zuccotti, Susan. 2000. Under His Very Windows: The Vatican and the Holocaust in Italy. New Haven and London: Yale University Press; ISBN 0-300-08487-0, pp. 59, 81, 93, 200.
- Riebling, Mark (2015). Church of Spies:The Pope's secret War Against Hitler. New York: Basic Books. p. 9. ISBN 978-0-465-02229-8.
- Riebling, Mark (2015). Church of Spies:The Pope's secret War Against Hitler. New York: Basic Books. p. 10. ISBN 978-0-465-02229-8.
- Riebling, Mark (2015). Church of Spies:The Pope's secret War Against Hitler. New York: Basic Books. pp. 9–10. ISBN 978-0-465-02229-8.
- Cornwell, John, Hitler's Pope: The Secret History of Pius XII. Viking Press (1999); ISBN 0-670-87620-8, pp. 149, 349.
- Peter Hoffmann; The History of the German Resistance 1933-1945; 3rd edn. (1st English edn); McDonald & Jane's; London; 1977; pp. 161, 294
- Phayer, Michael. 2000. The Catholic Church and the Holocaust, 1930–1965. Indianapolis: Indiana University Press; ISBN 0-253-33725-9, pp. xvii, 57, 102, 166-167, 176, 199, 207, 221, 237, 239.
- Phayer, Michael. 2008. Pius XII, The Holocaust, and the Cold War, Indiana University Press; ISBN 978-0-253-34930-9, pp. 177, 206.
- Dwork, Debórah, and Pelt, Robert (January 2002), Holocaust: a history, p. 423.
- Cornwell, John. 1999. Hitler's Pope: The Secret History of Pius XII. Viking; ISBN 0-670-87620-8
- Phayer, Michael. 2000. The Catholic Church and the Holocaust, 1930–1965. Indianapolis: Indiana University Press; ISBN 0-253-33725-9
- Phayer, Michael. 2008. Pius XII, The Holocaust, and the Cold War, Indiana University Press; ISBN 978-0-253-34930-9
- Riebling, Mark, 2015. Church of Spies: The Pope's Secret War Against Hitler, New York: Basic Books, ISBN 978-0-465-02229-8.
- Zuccotti, Susan. 2000. Under his very Windows, The Vatican and the Holocaust in Italy. New Haven and London: Yale University Press; ISBN 0-300-08487-0
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