The Nice attacker "... did not seem overtly religious. Locals said he was often seen drinking beer and never attended the small mosque near his block of flats. ... had been in trouble with police between 2010 and 2016 for threatening behaviour, violence and petty theft. In March, a court in Nice convicted him of assaulting a motorist with an improvised weapon - a wooden pallet ... "
The Paris attackers (the two Abdeslam brothers, one who blew up himself, and the other one who was arrested) owned a bar serving alcohol and were not religious either. They did not attend a mosque. There were drugs in that bar too, and neighbours complained.
Source: Business Insider.
Other attackers also got in trouble with the law: petty crime, drug dealing, ...etc.
This seems like a recurring theme with Islamic State now. They don't recruit from religiously observant people, like Al-Qaeda used to do. They recruit ex-criminals, apparently seeking salvation by committing a 'martyrdom act'.
But don't let facts stand in the way of prejudice and preconceived ideas ...
From another immigrant Canadian ...