Night Train (2009) on Netflix

Two Passengers and the conductor discover that a person has passed away on their Night Train cabin. They come across valuable diamonds on his person, that they wish to keep for themselves. So, to make it look like the man never boarded the train, they conspire to dump his body in a river that the train passes. Their scheme to get rid of the corpse escalates to the point where they have to chop up his body just to fit him into a small trunk. They then become paranoid, as they might turn on each other.