Complex sentence: For the first of only two times in all their train robberies, the outlaws robbed the passengers; in both instances, their usual target, the safe in the baggage car belonging to an express company, held an unusually small amount of money.
Split into simpler sentences: For the first of only two times in all their train robberies, the outlaws robbed the passengers. In both train robberies, their usual target, the safe in the baggage car belonging to an express company, held an unusually small amount of money.