Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
"The Killers" is presented to us rather nakedly. Here’s what happens, judge for yourself. The author’s attitude towards the work, then, is basically neutral. If the reader feels sympathetic, it’s because the reader is compassionate, not because the tone encourages sympathy. This really fits the bill as far as the story goes; if "The Killers" is about an encounter with unadulterated evil, then it should be presented to us in an unadulterated manner. Or, to put it another way, we as readers encounter "The Killers" the same way Nick Adams encounters the killers.