Philosophy of law riddle

Odd how things crop up; this week one particular 'riddle' has been presented to me in various contexts and in slightly different ways. In essence it goes as follows -

Adam, Bill, and Charlie are in the desert. Bill and Charlie want Adam dead. Bill unbeknownst to Charlie poisons Adam's water canteen. Charlie steals Adam's canteen. Who killed Adam?

Supposedly some deep unanswerable question, but I don't see the problem. Take three universes. In Universe Adam both Bill and Charlie act as described; in Universe Bill only Bill acts; in Universe Charlie only Charlie acts. At the end of all actions does the state of any of the Universes correspond?

In Universe Adam, Adam has lost his canteen.
In Universe Bill, Adam has his canteen, but it's been poisoned.
In Universe Charlie, Adam has lost his canteen.

We'd have no problem declaring Charlie the murderer in Universe Charlie so Charlie is also the murderer in Universe Adam. Bill is just guilty of attempted murder. This can be extended further -

Adam, Bill Charlie, and Derek are in the desert. Bill poisons Adam's canteen. Charlie empties the 'water' and replaces it with sand; Derek drills a hole in the base so the 'water' will leak out.


In Universe Adam, Adam has an empty canteen.
In Universe Bill, Adam has his canteen, but it's been poisoned.
In Universe Charlie, Adam has his canteen, but it's full of sand
In Universe Derek, Adam has an empty canteen.

Derek is the murderer.