Gitta Sereny, an Austrian-born English journalist whose work, which included portraits of Nazi war criminals and studies of youthful murderers, repeatedly and sometimes controversially sought to illuminate the wellsprings of evil, died on June 14 in Cambridge, England. She was 91....

A resident of London who had lived most recently in Cambridge, Ms. Sereny (pronounced suh-REE-nee) was long considered one of the foremost investigative journalists in Britain. She was known for her tenacity, her willingness to sit down with some of the most reviled figures of the era and her long, probing interviews — sometimes spanning years — that could prompt her subjects to reveal extraordinary things about themselves.

Among her best-known books are “Into That Darkness” (1974), about Franz Stangl, the commandant of the Sobibor and Treblinka extermination camps, who was responsible for the deaths of 900,000 people; “Albert Speer: His Battle With Truth” (1995); and “Cries Unheard: Why Children Kill,” about Mary Bell, an Englishwoman who as a girl in the 1960s murdered two young boys — a book that caused a furor when it was published in Britain in 1998....