Originally Posted by SuperChuck
Depending on your use of judgment, you can be considered at least partially responsible. You didn't pull the trigger, but if you decided to be a hero or a fool, your action indirectly resulted in death. If a member of your family were to be taken hostage in such a way, you would want everyone to remain calm and cooperate; if some hothead did something stupid, you would certainly hold him responsible. There's some amount of judgment involved.
Similarly, if someone is driving on the wrong side of the road, causing another driver to swerve off into a telephone pole, the driver on the wrong side of the road is responsible. That driver did not directly do anything which directly affected the other driver (in fact, he never touched him). The other driver could have made a move that would not involve driving into a pole.
We hold other nations responsible for their indirect actions. Selling weapons to insurgents, for example. There's even some talk about blaming Iran for suggesting to Hezbullah that they could capture an Israeli soldier. These are things that aren't done directly, but that hold indirect responsibility.