Complex sentence: On September 6/7,1939, Bochnia was defended by several Polish units, and soon afterwards, one of the first mass executions in occupied Poland took place in the town, in which Germans shot 52 Poles as a reprisal for killing two German Police officers.
Split into simpler sentences: On September 6/7,1939, Bochnia was defended by several Polish units. One of the first mass executions in occupied Poland took place in the town: the Germans shot 52 Poles as a reprisal for killing two German police officers.