The Hinterkaifeck Murders

In the pre-Nazi Germany of the early 1920s, farmer, his wife, daughter, grandson, the family maid, were all found brutally murdered with a weapon that resemble md a pickaxe. Over one hundred years later, amateur sleuths are still trying to figure who may have been the cold-blooded murderer of this family. Did the Gruber family have any secrets that could have led to their demise? Or were the killings merely perpetrated by a transient traveling the German countryside?