Classicly

Mike was still for perhaps two seconds, while his brain raced. Then he sent a tiny pencil-beam at the vault door. It was closed, solidly. No one had been before him. But there was a man bound hand and foot.... 

The light played upon him again. He was a young man, dressed as if he were a clerk or a bookkeeper in the factory. His eyes blinked and stared imploringly at Mike. There was some message, some terrible message, that he struggled to convey, but the gag prevented him. Mike watched him for an instant in mounting uneasiness and suspicion.