A detailed and long analysis piece by Raffaello Pantucci 'What Have We Learned about Lone Wolves from Anders Behring Breivik?'. The abstract says:
Anders Behring Breivik’s massacre on July 22, 2011 showed the danger that a well-organized Lone Wolf could cause. The methodical and calculated way with which he prepared and justified his act awoke security services the world over as to the potential menace that this form of terrorism can pose. As they revise their strategies, this article casts a preliminary eye on the case using a particular Lone Wolf prism of analysis to try to see what lessons can be learned from the case. Drawing on Breivik’s own writing and public sources, the article analyses his biography, the ideology he used to justify his act, the degree to which he seems to have been connected to others, his effectiveness, what role the Internet played and his mental competence all to try to draw some early lessons from the case. In concluding it offers some possible lessons learned that might offer practitioners some ideas of how to counter this sort of a threat in the future.
Link:http://raffaellopantucci.com/2011/12...hring-breivik/

He concludes:
From the perspective of countering people going down Breivik’s path, it is almost impossible to imagine solutions without moving into the space of curtailing individual free speech rights something that is clearly counter-productive. However, some recognition of the potential for such virulent language to be taken further into action by certain individuals is important. Mainstream political parties should make greater efforts to counter it through debate when they see it emerge. A parallel case to be considered in this light is that of Congresswoman Gabrielle Giffords in the US. She was shot by a man who thought he was doing his part to support the extreme right of his party that had attacked Congresswoman Giffords as a traitor for holding certain views. Ideas and words have great power and in a world where we can see the ease with which terrorist operations can be launched by individuals without much outside direction, consideration must be paid to the fact that such extreme ideas might resonate in different ways than they are intended. While stamping out such ideas and thoughts is going to be impossible, currently in some European countries, such ideas have been allowed to slowly move into the mainstream with little confrontation from established political entities. More effort could be expended to confront such ideas and prevent them being mainstreamed. The result otherwise is likely to be more Lone Wolf attacks in the future with a few managing to get through with results as spectacular and tragic as Anders Behring Breivik’s.
To say the least an investigative nightmare, even with modern techniques, notably in IT systems doing the initial analysis - so many leads to check.