It was Friday's evening, and the time was coming close to the moment Shu Xue would be closing the store. Her boyfriend, Zhao Wentu, had finished his evening lecture and was already waiting to walk her home. Just as she was putting some change into the cash register, one of the last few clients, a man wearing a mask and a hood disguising his appearance, walked up to her. She saw something in his eyes, covered by the shadow of the hood, that made a warning alarm go off in her head.