Conundrum 4-Causation!

Here is another one!

THIS IS A HYPOTHETICAL: Henri plans a trek through the desert. Alphonse, INTENDING to kill Henri, puts poison in his canteen. Gatson also intends to kill Henri but has NO idea what Alphonse has been up to. He (Gatson) puctures Henri's canteen which contains the poison of Alphonse, and Henri dies of thirst! Who has caused Henri's death? Was it Alphonse? How could that be, since Henri never swallowed the poison. Was it Gatson? How could that be, since he only deprived Henri of some poisoned water that would have killed him more swiftly evan than the thirst. Was it neither than? But if nether had anything to do with it, than Henri would still be alive! SO WHO KILLED HENRI?

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