Would either party be guilty?

This isn't a "serious" legal question. It's a brain-teaser I heard years ago. But unlike most brain-teasers, it is more about stimulating a discussion than about figuring out the "right" answer.

Adam, Ben, and Chuck are stranded at a desert oasis. Adam announces that in the morning, he will try to travel on foot to the nearest town. He fills his canteen with water before going to sleep.

Ben, who hates Adam, secretly pours some poison into Adam's canteen during the night. The poison will kill Adam instantly if he drinks it.

Chuck also hates Adam and is unaware of Ben's actions. In the morning, just before Adam starts out, Chuck drills a small hole in the canteen, hoping that Adam will die from lack of water.

Adam begins walking across the desert, and when he first tries to take a drink, he discovers that his canteen is empty. He dies of thirst.

Eventually, this all comes to light and Ben and Chuck stand trial for murder.

Ben argues that he is not guilty, since Adam did not drink a single drop of the poison which Ben put in the canteen. Ben argues that he is therefore not responsible for Adam's death.

Chuck argues that draining the canteen of poisoned water only served to prolong Adam's life and to give Adam a better chance of making it back to civilization alive. Chuck argues that depriving a man of poison is hardly murder.

It seems that each are guilty of attempted murder, but are either of these two actually guilty of murder? Is the legal answer different from the ethical answer? Ten points for the most convincing argument.