Journalists and writer Gitta Sereny, known for her books about the nature of evil, has died age 91.
Author Blake Morrison told the Today programme that she was someone "who always wanted to understand more, to dig deeper".
"She was a one-off... I don't think there anyone else like her," he said.
Thought For The Day contributor Rev Giles Fraser, said books made you see your own reflection in evil people.
"It is a terrifying journey... you see that evil is looking more and more like you," he told Evan Davis.
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