Between 12,000 and 15,000 people from more than 80 countries have gone to fight in Syria since the beginning of the uprising there in March 2011. Some have now moved on to Iraq or elsewhere, but many have gone home. Their countries are struggling to know how to deal with them, with most governments seeing them as a serious threat to national security.
The progression from being a foreign fighter in Syria to becoming a domestic terrorist at home is by no means linear, and certainly not inevitable. Many foreigners have no intention of going home, and some have died fighting. Others are horrified by what they have seen and just want to get back to their previous lives.
Disillusioned fighters can make excellent spokesmen against radicalizing propaganda.
But there will be some who have either become so radicalized or traumatized by their exposure to the ideology and violence of extremist groups that they may well pose a threat when they get home.
The problem for their countries of origin is to know which ones present a risk and which ones do not, especially where the capacity to investigate and monitor them is limited.
One way to help make these vital distinctions is to understand more about why so many young — and sometimes not so young — people have decided to go join the battle.
It will also help to know what sort of radicalizing or de-radicalizing influences may exist once they get there, depending on where they are fighting and with whom. And perhaps most importantly, it will be useful to know as much as possible about why some decide to go home.
The best way to make some sort of assessment of the motivation of foreign fighters, and the changes in their attitudes over time, is to ask them. This may seem an unlikely way to collect data because most foreign fighters who return home will probably make every effort to do so unnoticed, hoping that the authorities never find out where they have been or what they have been doing.
But given the attention all countries are now paying to their nationals who have gone to Syria, or may be thinking of doing so, it is likely that many of the returnees will be known and the authorities will be on the lookout for their reappearance.
Some governments, and Russia is one of them, have already adopted legislation that criminalizes unauthorized participation by their citizens in a foreign war, and the first objective of the authorities will be to put any returning fighter before the courts.
But even in these cases, a lot of useful data may be learned through discussion with the returnee about his motivation and experiences. This should not be in the form of an interrogation or of an interview seeking evidence of a crime, but more as a way to assess the long-term risk that the individual may pose, whether as a radicalizing influence in prison if convicted, or in his home community if released.
There are several other benefits from this approach. Countries all over the world have tended to deal with terrorism as a crime to be prevented or punished, without doing much to understand what lies behind it. Countering violent extremism is a policy initiative in many regions of the world, but it still suffers from a lack of empirical research into what leads people to become violent extremists in the first place.
The reasons are often very personal, and so vary from individual to individual, but there is likely to be a large enough area of overlap to provide a practical basis for the formulation of policy. This is not an argument for going soft on terrorists so much as a practical approach to limiting their appeal and impact on society by finding out more about the processes of radicalization.
Another benefit can be in helping the design of rehabilitation and reintegration programs in the several countries where these exist or are planned. Families generally play a key role in these programs but are often overwhelmed by the emotional difficulties involved.
A clear understanding of the dynamics that led a son or daughter to join an extremist group abroad, and of the sort of things that he or she may have experienced, would be of real practical assistance in helping families deal with the problems of re-acceptance.
Furthermore, fighters who have become disillusioned can make excellent spokesmen against the radicalizing propaganda put out by violent extremist groups.
They have infinitely more credibility with the target audience than someone who has never been involved. They know what extremist messages have appeal, and to whom, and they can reach those vulnerable people far more easily than any official is able to.
For these reasons, the United Nations intends to mount a worldwide survey of returned foreign fighters. Participating states, and it is hoped that Russia will be one of them, will have significant input in the design of the methodology as well as direct access to the results.
Although the threat from many of the more than 800 Russians who have gone to Syria is obvious and well known, there will be others whose motivation is less clear.
It will surely be of value to have a better understanding of what it was that made them take such a drastic step.