Difference between killed and died
I wondered whether my blunt answer would be contentious. Maybe I should modify what I said and substitute "wrong to say" with "inappropriate to say", because I think that "killed" often sends the wrong message.
Let me try to clarify that with a few examples:
A man gets lost in a desert and eventually expires from dehydration. It would be inappropriate to write a headline saying "Man killed in desert" because that would immediately suggest that the man had been murdered.
A policeman arrives at the scene of a car accident where there has been a fatality. No other drivers or cars were involved. Again, it would be inappropriate to write that the deceased driver had been killed. Better to say that he died (the scene of) the accident.
However, if a rally driver deliberately aimed his car at spectators, then I think it would be correct to use the word "killed" when describing how the victims had met their deaths.
To summarise, I think that the difference between "killed" and died" is that "killed" almost always involves an active agent, whereas "died" is more of an observation (perhaps leaving any judgement of the circumstances open to the reader). So your comrade could be killed by a stray bullet but passengers in an aircraft are not killed by a pilot who has a heart attack.
Martin - I have not trawled all the dictionaries, but my favourite, Chambers dictionary, begins (thus in my interpretation defining the most important meaning) with: To murder or execute; to deprive of life; to destroy; to nullify or neutralize...Incidentally I think that the point is made clearer by the related noun "killer" which Chambers defines as a person, creature or organism, chemical, that kills...