What time of the day was this visit to the store?
What day of the week? Around a holiday, or similar?
Can we get a physical description? Height weight, skin color, hair style, odor?
A facial sketch?
Some of the small stores are in highly dense small shop areas, and asking with a sketch at other store maybe a benefit - possibly also additional visual evidence such as videos.
What was he wearing? Clothing tells a lot about a person.
Jewelry, watch? Socio-economic grouping.
Cell phone, possible brand? Possible cell tower info.
Was he talking on the phone?
What was his demeanor?
What was the weather like?
Presuming the public transport was used, the radius, or corridor around the transport can be narrowed or widened.
Was he carrying any bags? Grocery bag, gym bag?
Tattoos, markings? This can give age range, possible organizational belonging, either military or gang or similar…
Already asked, cash or card payments?
What was purchased?
Is there gas station attached to this store?
Was it established that this person used public transport, and not a personal transportation?
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Presuming this happened yesterday and I was LE - and this was crucial, I would get the time and date, and get all the cell towers that cover the store. the narrower the time frame the less work to do.
Then get all the connections for that time on those towers, and work backward from that.