Vera Kriegel and her twin sister Olga were just five years old when they were taken from their village in Czechoslovakia to Auschwitz. 

Transported in cattle cars which were so tightly packed that the dead were still standing, she recalls the "sheer terror" of arriving at the camp and treading on "dead people like steps" as she left the train.

New arrivals at the camp were sorted into the weak, who would be gassed straight away, and the strong, who would be made to work. But Mengele and his assistants were there too, looking for twins.

Vera, her sister, and her mother were taken straight to SS Captain Josef Mengele. He was intrigued, she says, by what he described as her mother's "perfect Aryan features" and blue eyes, while Vera's and her sister's were brown.

Mengele selected them for experimentation....