When Milo Rau was approached by a Belgian arts centre to make a show with a young cast of actors, he asked himself what it was that most concerned that country’s children. “I added one and one together and came up with Marc Dutroux,” says the director. Dutroux is the imprisoned Belgian paedophile and murderer who in the mid-1990s kidnapped and raped six girls, killing four of his victims. The show, Five Easy Pieces, features one adult and seven children under the age of 12 who take on the roles of the murderer, his victims and an investigating policeman.

“Maybe if I hadn’t trained as a sociologist before I started making theatre I wouldn’t have had the idea,” says Rau, whose company goes by the name of the International Institute of Political Murder. “But when I make a piece of theatre I use the same methodology that a sociologist would use. If I’m doing a play about Putin’s Russia or Congo, I go there, talk to the people and sometimes even invite them on stage. For me the Dutroux case marked a moment of cultural change. I was interested in looking at what we find out about ourselves when we let children tell this story back to us.”

It sounds like the kind of project guaranteed to cause outrage. Rau’s most recent piece, a stage version of 120 Days of Sodom featuring a learning disabled cast, has already attracted the ire of the Daily Mail. But Five Easy Pieces is a reasoned, highly Brechtian piece of theatre and the very opposite of sensational. When I watched a video version I found myself not only moved but also laughing out loud quite a lot.

“It’s supposed to be funny,” says the Swiss director, speaking on the phone from Berlin, where he is based. “It’s a funny way of talking about sad things. Doing it with children heightens the way it can be humorous and serious and heartbreaking at the same time. When a child puts on a policeman’s uniform they do it in a way that makes you understand the absurdity of all uniforms. I often think that we human beings are a very strange tribe of people.”

Rau’s 2009 show The Last Days of the Ceausescus recreated the dying days of the communist Romanian dictatorship, putting the audience in the position of witnesses to a scenario of revolution, betrayal and chaos; Hate Radio – the only previous Rau show to be seen in the UK – looked at the role played by the broadcaster RTCM in the Rwandan genocide; and Empire, the third part in Rau’s European trilogy, puts refugee stories on stage and asks what Europe will look like in the future.

Facebook Twitter Pinterest Milo Rau in 2015 during the run of his show Compassion, History of the Machine Gun at the National Theatre of Brittany in France. Photograph: Jean-Francois Monier/AFP/Getty Images

“I’m always searching for the traumatic, tragic moments in individual lives and a country,” he says, “because it’s in those moments we are most touched and most changed.” He believes that the current paranoia against elites and the populist movements of Europe can be traced back to the mid-1990s and the horror and unease felt with the uncovering of the Dutroux case. “Belgium was a country dealing with loss. It had been the most important mining country in the world and that was over. People were starting to realise that the past was never coming back and the future would look very different,” says Rau who suggests that disquiet over the role of government in the end of the mining industry then fed into anger felt over the Dutroux case and the opportunities missed by the police to capture him earlier. People were looking to find someone to blame.

“The Dutroux case made people question what the government was doing and what it hadn’t done.” He says that he has talked to the children involved in Five Easy Pieces about the terrorist attacks in Paris and Brussels, and wonders whether for them and their parents this is not another Dutroux moment in which shock and horror turns to interrogation about the competence of the authorities and government.

“Once again, people are asking why doesn’t the government work? It’s the same story repeating itself on another level. There is a certain paranoia that is bred when you feel marginalised or on the periphery of the world, particularly one that is changing so fast.”

Five Easy Pieces reflects those feelings, and it’s no surprise that it has been co-commissioned (with Ghent company Campo) by one of the UK’s most provocative and challenging festivals, the Sick! festival, which this year has an impressive roster of shows probing the nature of identity and what it means to belong in a conflicted world. Rau’s piece explores how we construct personal identity at times of national trauma, and to do so it uses the same sort of format as Five Easy Pieces, written by Stravinsky as a piano primer for his children.

Facebook Twitter Pinterest The young cast of Five Easy Pieces. Photograph: Phile Deprez

Children do need protecting. We had a lot of material, some of it very dark, and we didn't share that with them Milo Rau

“The lessons the children have to master on stage get more difficult as they go on. The first lesson is mimicry, a task in which a child has to play an old man. But gradually the tasks get harder and include submission, emotion and grief. Our fifth lesson is rebellion, a rebellion that is poetic and allegorical.”

Rau was shocked to discover how much the children already knew about the Dutroux case but nonetheless felt protective of them. “Children do need protecting. We had a lot of material, some of it very dark, and we didn’t share that with them.” There have also been psychologists on hand throughout the process to ensure the children’s and their parents’ wellbeing.

But what about those directly connected with the case, some of whom – including Dutroux’s father and some of the victim’s families – were interviewed for the piece? Jean Lambrecks, the father of Eefje, oldest of the girls murdered by Dutroux, has said the show “hurts the truth”.

Rau is full of compassion for the man who lost his daughter and says: “I was in constant exchange with him, and right from the beginning I told him that the case is the starting point, but we cannot cover every aspect of it. It’s not a documentary play. In fact the Dutroux case is not the theme of the play, it serves as an allegory about how we think and feel about the world and how we deal with trauma. But this man, he lost his child, so of course for him it is different, for him every detail must be present.

“I have made lots of plays that begin with something that really happened, and when you do that people will always say ‘but you left out that bit.’ I understand that, but I also know that if I were to make a play about the Earth, some people will ask why this play doesn’t include the moon. It is always the way.”