The technique used by the author to build suspense in the excerpt is "The outcome of events becomes uncertain." The excerpt sets up the expectation that the narrator will be leaving the theater soon, but that expectation is disrupted when the exit door suddenly goes dark and a deadbolt is heard locking. This creates a sense of uncertainty and tension in the reader, as they are left wondering what could be happening and what the outcome will be. The outcome of the situation is not revealed in the excerpt, leaving the reader to speculate and prolonging the suspense.