In a dark corner of Poland that refuses to acknowledge its horrific treatment of Jews, an amateur photographer is reopening old wounds by tracing ghosts in her home town.Katarzyna Markusz focuses her lens and all her attention on a concrete slab at the far edge of a neighbour’s yard in Sokolow Podlaski. She squints her eyes as she presses the shutter button. It seems she cannot stop taking photographs of this small town in the Polish hinterland.It is June and I have come here to see Markusz’s exhibition of photographs in a cafe next to the town’s cultural centre. The exhibition, entitled Missing, has focused attention on a raw nerve – Sokolow’s Jewish heritage.Markusz, a 28-year-old amateur photographer and mother of Michal, nine, and Andrzej, two, began researching the history of the town for her exhibition in 2009 and it has taken over her life.Like her photographs, there is an air of sadness about Markusz. Her husband cannot fathom her obsession with the Jews who once inhabited this town 80 kilometres east of Warsaw, one of whom was Joseph Rubenstein, the father of Lee Harvey Oswald’s killer, Jack Ruby.