Few details are yet known about the attackers, but Mohammed Karabila, a local Muslim leader, told the Associated Press that one of them had been "followed by police for at least a year and a half". That person is believed to be Adel K.
The French ITele website said he had tried to reach Syria in May 2015 but was turned back at the Turkish border.
According to the report, he then spent nearly a year in prison before being released in March, on condition he wear an electronic tag and move back in with his parents.

Where is John Oliver to make smarmy jokes about how it's racist and paranoid to not want 2 million random foreigners with terrorists intermixed let in to your country?

Build a wall out of Mexicans