On Tuesday 27 January 2015, European heads of state and former inmates of Auschwitz will commemorate the 70th anniversary of the camp's liberation.

Nazi Germany murdered approximately 1.1 million people at Auschwitz, mostly Jews, but also Poles, Roma, Soviet prisoners of war and gays.

The anniversary raises painful questions for residents of Oswiecim, the town in Poland where Nazi occupiers created one of the most relentless extermination machines in history.

How could their parents go about their daily business when such inhumanity was taking place just the other side of a barbed wire fence? How much did they know of what was going on?

"Of course people knew what was going on," said Bogumila, who lived through the occupation as a child. The mass extermination of prisoners and the incineration of thousands of bodies, she said, were no secret.

Some describe having to live with the stench from bodies being incinerated at Auschwitz, but keeping quiet to survive.

Between 1940 and 1945, Auschwitz developed into a vast complex of barracks, workshops, gas chambers and crematoria.

Seven decades on, Oswiecim is trying to put the bleak past behind it, a giant "City of Peace" banner displayed next to the main railway hub, which once saw hundreds of thousands transported in cattle wagons into the camp's gas chambers.