Nikolas Cruz -- the alleged shooter who killed 17 people at a Florida high school -- casually blended in with fleeing students while making his getaway ... then stopped at Subway for a drink.
Law enforcement says Cruz entered a nearby Walmart shortly after ending his shooting spree and went inside to order a drink at the Subway inside the store. He then left the store on foot and walked to McDonald's, where he laid low for a few minutes ... before taking off on foot.
Cops caught up with Cruz about 40 minutes later and arrested him.
As we reported ... Cruz made online threats about a mass campus shooting 9 months ago, and was even reported to the FBI for more disturbing YouTube comments back in September.