I think we way over-think this stuff. There was a jihadi knife attack at a mall just last weekend, jihadi bombings in New Jersey and New York last weekend. This radicalized Islamic kid with family roots back somewhere in Islamic lands uses a method he knows and is familiar with - maybe he has help, maybe not - he walks in executes his attack quickly before an alarm can be raised, hitting the first place he comes to. He shoots his ammo, drops the weapon and gets out fast, well before any police could get close to responding, runs off in his pre-planned escape route...maybe with help and maybe not...and disappears. He becomes a hero in his world.
2 cars searching the Milltown area north of Stanwood.