I'd also like to point out, and anyone who has ever worked at a small town gas station I would think agree, that it develops it's own little subculture. The lotto tix, ciggs and cheap food (beer & wine in some states) it starts to act as a hub for people on a lower income, as they usually can walk there from home, need inexpensive food ect, and feed their habits (ciggs, booze or whatever you can score). It is a weird position for the store owner to be in because these are your best customers, but you know there is illicit activity going on so you must find a way to accommodate your main source of income and stay within the law to some extent to keep your business operating.
This is one reason why I don't find AA's behavior and knowledge of JC's purchases odd.
I do find it weird that if she were comfortable enough with him for him to believe if someone gave her a problem outside of the store she would have told him, (which is how I understood his quote) that she would only say she is going 'somewhere'. She was intentionally vague with him if this is correct, so he might not know the killer or it might have been someone he doesn't get along with.
Just some thoughts I hope help

MOO JMO etc etc