This shit seriously can't be stopped.
You can stop thousands getting killed - 9/11 - possibly stop hundreds killed in subway attacks.
But, how the hell do you stop 2/3 guys getting out of the house with a AK - 47 - multiple clips of ammo and just stopping at a random restaurant and killing maybe 5/10 people at each location
Wear people down through the sheer terror and attrition. No need for huge networks, money or planning.
feck being a politician or a security official in charge of stopping this type of terrorism