And as the BRU attackers may have done, they caused an explosion at one area and then a bit later hit another area that could be and was used as an entry/exit to escape the area.

Bottlenecks and herd creations make it more easy for criminals and nutcases to attack as if shooting into a barrel full of targets. But the security forces at airports that have these kind of major bottlenecks and herd pens in many places are de facto protecting physical infrastructure more than human lives whether they know it or not.

The BRU suspects on the CCTV feeds are expected have a history of being rather secularized criminal rebel types with a taste for video game playing, drug-dealing, drug-using, getting drunk, stealing, being pimps/johns and engaging in other such behavior that is more a pattern in line with the Paris 2015 attackers than any Friday-Sunday life-long devout religious types. Any guess on which video games they've played? I doubt it was Flight Simulator, as that doesn't focus on public places being used to shoot-up and otherwise kill people.