Gitta Sereny, CBE (13 March 1921 – 14 June 2012) was an Austrian-British biographer, historian, and investigative journalist who became known for her interviews and profiles of infamous figures, including Mary Bell, who was convicted in 1968 of killing two children when she herself was a child, and Franz Stangl, the commandant of the Treblinka extermination camp.

Born and initially raised in Austria, she was the author of five books, including The Case of Mary Bell: A Portrait of a Child Who Murdered (1972) and Albert Speer: His Battle with Truth (1995).

After the Nazi takeover of Austria in 1938, she moved to France, where she worked with orphans during the German occupation until she had to flee the country because of her connection to the French Resistance.

The book was also later adapted by David Edgar as the play Albert Speer and directed by Trevor Nunn at the National Theatre in 2000.

This led to her covering the trial of eleven-year-old Mary Bell (found guilty of murdering two children) and would further lead to her first investigative book on this case.

Into That Darkness (also following an initial article for the Telegraph magazine) was an examination of the guilt of Franz Stangl, the commandant of the Treblinka and Sobibor extermination camps.

However, Sereny concludes that Speer must have known based on a letter he wrote to the Jewish community in South Africa (after the war), and the fact that his closest assistant attended the Wannsee Conference (where the details of the genocide of the Jews were worked out) and could not have failed to inform him about the proceedings.

"[12] British Holocaust denier David Irving initiated a libel case against Sereny and the Guardian Media Group for two reviews in The Observer where she asserted he deliberately falsified the historical record in an attempt to rehabilitate the Nazis.

Irving maintained a personal animosity for Sereny, whom he calls "that shriveled Nazi hunter", for successfully refuting his claims since the publication of his book Hitler's War.