Philosophical question: who is guilty in this situation (see details)?

Inspired by this question.

Here is a classic problem in philosophy and law used to challenge students. It concerns causation, preemption, and overdetermination. I am interested in your thoughts on it:

Everybody in the French Foreign Legion outpost hates Fred and wants him dead. During the night before Fred’s trek across the desert, Tom poisons the water in his canteen. Then, Dick, not knowing of Tom’s intervention, pours out the (poisoned) water and replaces it with sand. Finally, Harry comes along and pokes holes in the canteen, so that the “water” will slowly run out. Later, Fred awakens and sets out on his trek, provisioned with his canteen. Too late he finds his canteen is nearly empty, but besides, what remains is sand, not water, not even poisoned water. Fred dies of thirst.

Who caused his death?

There are many variations of this problem, some of which are more elaborate than others. The version above comes from the paper “Who’s Afraid of Determinism?” by Christopher Taylor and Daniel Dennett, which can be found here.