Keep believing yourself, you'll get far in life, oh wait you won't.
1. France, Charlie Hebdoo Shooters (French nationalities)
https://en.wikipedia.org/wiki/Charli...ing#Assailants
https://en.wikipedia.org/wiki/Amedy_Coulibaly
2. France, November 2015 attacks (Belgian and French Nationalities)
https://en.wikipedia.org/wiki/Abdelhamid_Abaaoud
https://en.wikipedia.org/wiki/Salah_Abdeslam (and his brother)
3. Terrorist attack in Belgium (Belgian and Swedish Nationalities)
https://en.wikipedia.org/wiki/Ibrahim_El_Bakraoui
https://en.wikipedia.org/wiki/Najim_Laachraoui
https://en.wikipedia.org/wiki/Mohamed_Abrini
https://en.wikipedia.org/wiki/Khalid_El_Bakraoui
https://en.wikipedia.org/wiki/Osama_Krayem
4. Nice truck attack (Moved to Nice in 2005).
https://en.wikipedia.org/wiki/Mohamed_Lahouaiej-Bouhlel
5. Berlin truck attack (came to Europe through Italy in 2015).
https://en.wikipedia.org/wiki/2016_B...tack#Anis_Amri
6. Manchester Arena (born in Manchester, lived in Fallowfield, UK).
https://en.wikipedia.org/wiki/2017_M...mbing#Attacker
7. London Bridge attacks.
https://en.wikipedia.org/wiki/June_2..._Bridge_attack
1st grew up in the UK and lived there.
2nd grew up abroad, but lived in Ireland predating the Syrian crisis.
3rd lived and worked in or around London.
8. Catalonia attacks.
https://en.wikipedia.org/wiki/2017_Catalonia_attacks
1st lived in Ripoll, Spain, from the age of 4
2nd lived and worked in Ripoll, Spain
3rd been living legally in Spain since 2005
4th been living in Spain
5th unknown
6th Been in Spain since 2002
Let's do the math 23 total attackers:
21 attackers had European nationalities
1 attacker is unknown
1 attacker came into Italy in 2015.
So that's 91.3% of all European attacks since 2011 which were committed by attackers that lived, worked within European borders. The only thing that needs to be mentioned is that a few of them traveled between EU and Syria months before their attacks, but they were not part of the refugee streams.
Could the numbers change in the future, of course they can, but as of right now, seems that Europeans travelling to Syria or having travelled to Syria during the conflict, being a much bigger threat than the refugees, of course, this can change, and this does not include failed of foiled terrorism plots.