At the heart of her work lies an obsession with explaining evil and discovering what makes people commit monstrous acts.

This is a theme she has pursued in her two books about Mary Bell as well as her highly-acclaimed biographies of Hitler's friend and architect Albert Speer and the commandant of the Nazis' Treblinka death camp, Franz Stangl.

The 74-year-old writer is known for being a meticulous researcher whose compassion for her often unappealing subjects is matched by an unwavering drive to get to the truth.

Prior to Ms Sereny's latest book, Cries Unheard, it was her work on the Third Reich for which she was best known.

Knowing the Nazis

Born a Hungarian in Austria, Ms Sereny read Hitler's Mein Kampf aged 11. Four years later, she heard him address the Viennese in person.

Sereny: personal experience of Nazism

In 1945, she briefly attended the Nuremberg war crime trials where she caught her first glimpse of Speer - her future subject - in the dock.

Half a century later, Ms Sereny befriended Speer and his wife to try to find out exactly how much he had known about the Holocaust while he was working for Hitler.

Ms Sereny admitted to liking the former Nazi despite his delusions of innocence. But in her book, Albert Speer: His Battle with Truth, she presented a damning portrait of a man who knew about the plan to exterminate the Jews but went along with it because of his love for Hitler.

Methods queried

As with Cries Unheard critics asked what exactly was the nature of the author's relationship with her subject and if it had tainted her work.

In a radio interview Ms Sereny said: "'Did she get to be too close to him?' I think of this question very seriously, you know. But what is 'too close'?"

Despite the qualms about her methods, Ms Sereny's anti-Nazi credentials were never in doubt. This was particularly true after she produced a detailed rebuttal of right-wing historian David Irving's book which claimed that Hitler did not know about the Nazis' genocidal policies.

Mr Irving was so enraged by his adversary that he described her as looking like "a shrivelled little prune".

Children who kill children

In recent years Sereny has also written extensively about the murder by two boys of the Liverpool toddler Jamie Bulger.

The theme - what leads children to kill children - was one she had explored earlier in her 1972 book The Case of Mary Bell.

What has aroused the current furore is not so much her decision to return to the Bell case but her payments to the child killer for her help and recollections.

Ms Sereny has defended herself in an open letter to the mother of one Bell's victims.

The purpose of the book she explained "was not to re-live these terrible crimes, but to find some understanding of how they could happen".

She said she had given the money in order not to contribute to the cycle of abuse and exploitation, which she claimed had dogged Bell's life.