For the role of Lena, Gallenberger wanted "someone who is radiant, who brings in a strong, bright energy."
"I wanted light to go into the dark place," he said.
Watson was fascinated by the character's bravery, saying, "You would hope that in Lena's shoes you would do the same thing that she does, but you wonder! You go, 'Wow, would I be brave enough to do that?'"
As far as casting for Daniel, who's held in an underground torture camp beneath Colonia Dignidad, Gallenberger knew Daniel Brühl was the right fit for the part from the beginning.
Michael Nyqvist plays Paul Schäfer, the former German soldier who founded Colonia Dignidad, and produces the kind of "intensity" Gallenberger said was essential to the role.