His new film Colonia is touring China as part of the 4th Festival of German Cinema. [Photo provided to China Daily]

He says the locals, including political prisoners, former cult followers and relatives of murder victims, slowly opened their hearts to him and talked about things that still haunt them.

"The film is trying to make people, especially the youth, not forget about what happened in the past," the director says.

"The four years (of research)were like being a detective. I had to put the pieces together to get the true story. It was very exciting but also very sad. But it's the only way to go deep enough to find out what really happened."

The 110-minute feature, which opened in Germany in February, has received mixed reviews so far. While some hailed it as a thought-provoking film, others called it a superficial attempt "using a shallow romance" to unveil one of the darkest chapters in Chilean history.

But Gallenberger seems prepared for questions.

"There are a million different ways to tell the story. But what's important for me is that it is told in a way that hopefully reaches a big audience," he says. "I wanted to make a film for people who've never heard about Colonia Dignidad, and who normally wouldn't care about what happened in Chile in 1973."

He believes a mix of a thriller and romance is an effective way to realize such a goal.

To date, the global box office has given the film $2.5 million. In China, despite its limited release in theaters, 1.87 million watched Colonia on streaming site iQiyi.