You did a great job with the pacing and the atmosphere in this piece. It was creepy and thrilling, which is the hallmark of a good suspense/thriller story. Nice work!

The logistics of what happened were a little confusing for me. Jim went into the back room and took a nap so he didn't notice in the camera feed when "the old man at the counter dropped to the floor like a sack of flour." When he wakes up to close the store, he runs into the stranger, and sees the dead guy at the counter ... and then does "a double-take around the store where he saw the other patrons from hours earlier littered in the aisles he could see from the front. All lying lifeless on the floor."

But then at the end of the story, we realize the stranger is a girl who's there to kill Jim specifically for something he did in the past. Did she come into the store and murder all of the patrons just because? Were they connected to Jim as well? Was what happened with the old man's fall against the counter an accident, or was that also the girl? If that was the girl, she killed everyone, then hung out in the store, standing there for two hours while Jim took a nap?

Some additional clarity on how the events play out moment-by-moment would be helpful to increase the tension of the story.

Overall, I think you're off to a great start with this story. Well done!