Why did the police not suspect foul play?
Much as I love this film, I have always found the treatment of Dietrichson's death implausible. Walter hits him on the back of head. This blow would not resemble the injuries caused by him toppling a few feet from a slowly moving railcar. Surely even a cursory examination would have made the police suspicious? If he had fallen over the rail then the injury should be to the front of the skull.
Comments from anyone with forensic experience are highly welcomed