What percentage of terrorists in the recent attacks in Europe have ever held the refugee immigration status in any EU country?
I am primarily interested in the data for the last 3 years or so. Any reasonable definition of "terrorist" will do (perpetrator of an actually carried-out attack, arrests for both planned and carried-out attacks, whether actually convicted or just a suspect, etc).
It seems like a basic question given all the heated discussions around this topic, but I can't seem to find the answer anywhere. I've looked at the EuroPol reports, Global Terrorism Database, etc. I did find such data for the US (see 2nd chart on linked page) - surely something like this must exist for Europe?