At the moment, there is no evidence that any of the attackers are anything other than French Citizens. Therefore it is not possible to blame these attacks on the refugee crises. Yes some may have returned to France from Syria, but in the past home grown attackers would go to Pakistan before returning to their home countries. This is nothing new. Sneaking in on a false passport is also not something new.
What's new is the opportunity to blend in with 10.000 illegals daily. Yes, evading border controls was a thing in the past, but you still had a higher chance of getting caught. Now, terrorists can come and go as they please, because authorities are bogged down with the flood.
The cause of the refugee crises and the cause of the homegrown terrorism are both linked to Islamic State. However the refugee crises is a symptom and not a disease in its own right.
Yes, but it's a symptom that makes terrorists' job ALOT easier
As for the idea that IS would smuggle in attackers disguised as refugees from Syria (rather than recruiting attackers in Europe, training them in Syria and returning them to Europe) that frankly makes no sense. To launch this type of attack you need weapons, you need a base to operate from, you need knowledge of the local area. None of these things are available to a Syrian sneaking into Europe.
You're borderline insulting my intelligence, and you have not read the study I have linked. I doubt you even looked at the infographics. OF COURSE they're not going to smuggle 100% of their assets in from Syria. They can get guns and explosives from the black market here. They have agents and local contacts here already. What they can smuggle in (with the refugees) is potentially HUNDREDS if not THOUSANDS of trained, brainwashed veterans straight from the Syrian war. These people can contact and join local sleeper cells to become assets for future operations
The weapons need contacts in local black markets, and the ability to work as smugglers. Why would you use Syrians when you can recruit French citizens who can travel with less suspicion and also have the advantage of speaking French, which is kind of useful for logistics in France.
Again, French citizens in need of training travel to Syria, receive training, come back while authorities are busy with the refugees.
The base (a flat or house) needs to be rented or bought from someone. In Europe cash in hand landlords are kind of rare, so you realistically need a bank account in Europe. Again,Syrian's find that hard to get hold of.
They already have local contacts, the newcomers just seek them out
Knowledge of the local area, again, local recruit tops a Syrian.
Local helpers
Ultimately, focusing on refugees as a cause is a dangerous game because that ignores the real problem of home grown terrorists.
Refugee crisis is not a cause, but a damn good diversion to smuggle agents into and from Syria