An article to accompany a BBC radio programme this evening, by Gordon Corera, which opens with:
Can state-sponsored assassination work as a strategy? And can it ever be justified? Governments don't admit to it, but Iranian nuclear scientists know it happens - and it's not easy to distinguish assassination from the US policy of "targeted killing".
Link:http://www.bbc.co.uk/news/magazine-17353379

It is a "broad brush", historical article and I'll link the radio podcast another time.