A free report from The Soufan Group, the main author being Richard Barrett (Ex-SIS & UN), which has some proper insight. From the flyer:
The policy response so far has often focused more on prevention and punishment than on dissuasion or reintegration, but as the number of returnees increases, and the resources required to monitor their activities are stretched to breaking point, it will be important to examine more closely why an individual went, what happened to him while there, and why he came back. This paper attempts to provide some general context for answering those questions, and offers suggestions for policy development.
Link to the report (33 pgs):http://soufangroup.com/wp-content/up...s-in-Syria.pdf

The flyer:http://soufangroup.com/foreign-fighters-in-syria/