When is killing someone murder?

We have an interesting confirmation class this year, and they have a multitude of pressing moral questions .....

Persistently they have asked "what if you are a soldier, and you kill someone, have you broken the commandment thou shall not kill?" And if you do are you condemned to hell?" And "is there such a thing as a just war?". These questions are posed against the backdrop of politically inspired violence that is our daily experience and many have family members with in the armed forces who are participating in the violence. And then add to that backdrop the daily experience of starvation being used as a weapon against the weak and vulnerable, and that the average life expectancy is around thirty five - the effects of poverty and AIDS. Last week a twelve year old boy in a school where my son volunteers died of dehydration because his parents were too poor to buy sugar and salt to make an oral rehydration solution to keep him alive when he developed diarrhoea. Tragically this is not unusual.

I am at a loss at how to begin to give them a framework to consider these questions on murder and killing. There are no easy answers at any time, but just at the moment they are really of a personal nature to each of us.

Does anyone out there have any suggestions as to where I might begin?

I would so appreciate the help.