Investigators say the victim was using an ATM inside of the Express Food Mart in the 6300 block of Frankford Avenue around 3 a.m. Sunday.
That's when officers say the suspect demanded money from the man. And when he didn't give up his cash, police say the suspect shot the man in the leg.
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He was taken to the hospital in stable condition.
Police are still working to locate the shooter.
Anyone with any information is asked to call police at 215-686-TIPS.