Overdermination and causation

A spy, setting out to cross the desert with some key intelligence, fills his canteen with just enough water for the crossing and settles down for a quick nap. While he is asleep, Enemy A sneaks into his tent and pokes a very small hole in the canteen, and a short while later enemy B sneaks in and adds a tasteless poison. The spy awakes, forges ahead into the desert, and when he goes to drink from his canteen discovers it is empty and dies of thirst before he can get water. What was the cause of the spy's death? According to the counterfactual theory, neither enemy's action caused the death. If enemy A had not poked a hole in the canteen, then the spy still would have died by poison. If enemy B had not put poison into the canteen, then he still would have died from thirst. Their actions overdeter-mined the spy's death, and the pinprick from enemy A preempted the poison from enemy B.

In the beginning of the movie Magnolia, a classic causal conundrum is dramatized. A fifteen-year-old boy goes up to the roof of his ten-story apartment building, ponders the abyss, and jumps to his death. Did he commit suicide? It turns out that construction workers had installed netting the day before that would have saved him from the fall, but as he is falling past the fifth story, a gun is shot from inside the building by his mother, and the bullet kills the boy instantly. Did his mother murder her son? As it turns out, his mother fired the family rifle at his drunk step-father but missed and shot her son by mistake. She fired the gun every week at approximately that time after their horrific regular argument, which the boy cited as his reason for attempting suicide, but the gun was usually not loaded. This week the boy secretly loaded the gun without telling his parents, presumably with the intent of causing the death of his stepfather. Did he, then, in fact commit suicide, albeit unintentionally?
http://science.jrank.org/pages/8555/Causation-OVERDETERMINATION-PREEMPTION.html

Jordan