Police say it started with an argument between a female employee and her boyfriend in the front of the store. The man, later identified as 30-year-old Anthony Birch, followed the woman into the store by way of the back loading dock, where the altercation continued.
Investigators say, at some point, Birch pulled out a gun and fired a shot. A male coworker came to the aid of the woman and he was subsequently shot three times.
"What we believe happened is, at some point, a male manager, an employee of the store, about 35 years old, attempted to intervene," said Lt. Frank Vanor of the Philadelphia Police Department.
One bullet grazed the victim's head. Two other bullets hit him in the arm and chest. By Tuesday night, that manager was hospitalized in guarded condition.
No other employees or shoppers were injured.
Birch's girlfriend was not hit.
Fearing Birch might harm the couple's young children, police removed them from classes at Olney Elementary. The school was placed on temporary lockdown.
Holme Elementary School as well as St. Dominick's Elementary School were also placed in lockdown because of their proximity to the Kmart shooting.
Birch took off in a gold Nissan with a black door. He is said to be about 5 foot 10 inches tall and was wearing a black hoodie.
Rob Schippert, who works overnight, says the manager is highly regarded.
"He's a great guy, I'm really shocked. I'm stopping to talk to him now on my way home," Schippert said. "He was the one who helped me get a job here."
If you have any information about the identity or whereabouts of the gunman you are urged to contact police by callling 911.