Read the excerpt from a short story.

after two hours of a tedious cinematic production, the dim aisle lights flickered back on. having endured scenes of fake gore and the phony distress of deficient actors, i stood to leave with a measure of relief. i would breathe easy in the open air, away from the greasy odors and the sniffling man whose cough had noisily barked over the on-screen dialogue. my steps slowed as the queue of exiting patrons jammed the aisles. then the sliver of light from the exit door went dark. the theater was briefly silent, and i heard the unmistakable sound of a deadbolt locking.

what technique does the author use to build suspense in the excerpt?