The gunman stole nothing, police said.
Gore was transported to the Hospital of the University of Pennsylvania, where he died shortly afterward.
At a news conference Tuesday, Homicide Capt. James Clark said police had no motive as to who would want to kill Gore, a father of two small children who had no criminal history.
"He works every day, he has had no negative involvement with the police his entire life, so we don't know what this is about," Clark said.
Gore's father is a veteran police officer assigned to the Third District in South Philadelphia.
Investigators do not believe his father's job played any role in Gore's killing, Clark said.
The Fraternal Order of Police Lodge 5 announced a $5,000 reward in the slaying, said president John McNesby.
Police described the gunman as about 5 feet, 7 inches tall, weighing 160 pounds, wearing a gray hooded sweatshirt, a black baseball hat, blue jeans, and black boots.
He was armed with a silver handgun.
Authorities ask that anyone with information about the slaying call the Homicide Unit at 215-686-3334.
Contact staff writer Mike Newall at 215-854-2759 or mnewall@phillynews.com.
