It happened around 11 p.m. at the ShopRite at N. Front Street and E. Olney Avenue.
Police said surveillance cameras at the store captured the altercation and they are working to get answers about why the shooting happened.
Police said the 23-year-old victim works as a cart attendant and was in the parking lot about an hour before the store was supposed to close.
They said he got into an argument with a 30-year-old customer and that the customer ended up firing three shots, striking him in the stomach, left hand and arm.
The employee then ran into the store, according to investigators.
"Preliminary information is the shooter does have a valid permit to carry a handgun," said Chief Inspector Scott Small with the Philadelphia Police Department.
Police said he was alert and talking, and that medics rushed him to the hospital where he was placed in critical condition and underwent surgery.
"The 30-year-old shooter remained on scene and did cooperate with police, so we have the shooter's weapon," Small said.
Customers told Action News that a lot of the cart attendants who work at this store have various cognitive disabilities. It's unclear if that's the case with this victim but customers wonder if there was possibly a miscommunication.
"They hire them and put some meaning in their life and so they're out here now and they get shot?" said Michael Taylor, from Elkins Park.
"When you see violence around this area it's sad to say it but it's nothing new," added Frederick Holt, from Olney.
There are still questions about what was said before the customer pulled out his gun and whether he felt threatened.
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