Gitta Sereny, an acclaimed investigative journalist whose books about Nazis and murderers delved into the minds behind heinous acts of depravity and violence, died June 14 at a hospital in Cambridge, England.

Her death was announced by her publisher. No cause of death was disclosed.

Ms. Sereny, a Viennese native, came of age as Adolf Hitler rose to prominence in Europe and became one of the foremost authorities on the crimes against humanity committed by the Third Reich.

She also wrote renowned books about murders involving children who killed other children. A 1999 New York Times review of “Cries Unheard,” about a notorious British child murder case, called her book, “an extraordinarily important and powerful work.”

“It will agitate, provoke, and poke and prod your preconceptions,” journalist Alex Kotlowitz wrote in the Times. “It will, I suspect, make it impossible to look at children accused of violent crimes the same way again.”

Ms. Sereny’s best-known books, however, concerned the Nazi regime. It was a movement she knew intimately.

As a youth, Ms. Sereny was mesmerized by Hitler as a charismatic leader and attended his 1934 rally in Nuremberg, later admitting to CBS’s “60 Minutes” that she “screamed ‘Heil!’ with the best of them.”

Her infatuation turned to disgust as she matured. While studying at the Sorbonne in Paris, she aided members of the French Resistance movement. After World War II, she served as a relief worker for the United Nations, tending to children who had been liberated from the Dachau concentration camp. Later, her duties included recovering children who had been stolen from their families as part of the Lebensborn program, a Nazi effort to create an Aryan super race.

She later worked as a reporter covering the Nuremberg trials and was fascinated by the Nazi officers who told the court that their only crime was loyalty to the cause.

“The more I met individuals who had suffered quite appallingly, the more I wanted to meet the individuals who had done it to them,” Ms. Sereny once said.

As an author, she was best known for her candid interviews with Nazi war criminals. She spent hours interviewing Franz Stangl, the commandant of the Treblinka extermination camp where nearly 1 million people died, and Albert Speer, the architect, high-ranking Third Reich minister and Hitler confidante.

Her closeness to her subjects, however, led some critics to claim that she appeared overly sympathetic to some of the men who helped carry out Hitler’s genocidal Final Solution.

Ms. Sereny spent more than 100 hours with Stangl while he was in a German prison, serving a life sentence for his role at Treblinka. To ingratiate herself with Stangl, Ms. Sereny brought the ailing man homemade soup to lift his spirits.

In her 1974 book “Into That Darkness,” Ms. Sereny wrote that Stangl — an unrepentant Nazi — ultimately admitted to her that he felt guilty about killing thousands. He died the next day.

She was later contacted by Speer, who had read “Into That Darkness.” He offered to speak with her about his own experiences within Hitler’s inner circle.

She eventually agreed, beginning a project that lasted more than a decade and ended with her masterwork: “Albert Speer: His Battle With Truth.”

In a 1995 New York Times review, historian Claudia Koonz called Ms. Sereny’s book, “a veritable ‘Rashomon’ of Nazi genocide in which all voices emanate from a single narrator.”

At his Nuremberg trial, Speer was remorseful but said he was ignorant of Hitler’s plan to exterminate Jews. He was spared the death penalty and sentenced to 20 years in the Spandau prison for engineering a vast slave labor program. Coming to know Speer, Ms. Sereny said that she came to admire the man and found him to be sophisticated, articulate and intelligent.

Ms. Sereny wrote that Speer was driven by his “love” for Hitler, whom he regarded as a father figure. Under Ms. Sereny’s questioning, Speer contradicted his Nuremberg testimony and told her that he had been keenly aware of the Final Solution, and had done nothing to stop it.

Observing Ms. Sereny’s ability to extract secrets, the Nazi once said to her: “You are dangerous, aren’t you?”

Gitta Sereny was born March 13 in the early 1920s. For an author who probed her subjects to reveal facets of their private lives, Ms. Sereny fiercely guarded aspects of her own biography. In dozens of interviews, she never gave her real birth year, which was variously reported as either 1921 or 1923.

Her father died when she was a toddler and her mother later married the economist Ludwig von Mises.

Ms. Sereny gained notice as a journalist for her work covering the Mary Bell murder case. At age 11, Bell strangled to death two younger boys and mutilated their bodies with a razor.

Ms. Sereny came under some criticism from journalists after she admitted to paying Bell for her cooperation on the 1999 book “Cries Unheard.”

Ms. Sereny defended her work by saying that her intention “was not to relive these terrible crimes, but to find some understanding of how they could happen.”

Her husband, photographer Don Honeyman, died in 2011. Survivors include two children.

Ms. Sereny wrote in her 2001 memoir “The Healing Wound” that her obsession with disturbing crimes and what caused them could be traced to her experiences in World War II.

“People are made by the circumstances of their lives,” she wrote, noting that she was “deeply affected by what the Germans did. It was the worst kind of inhumanity, such an enormous wrong. . . . We lost a moral part of ourselves, and somehow we must regain this part. Maybe my way of regaining it is by doing what I’m doing.”