A family in Upper Darby is seeking justice after a teen was fatally shot on a SEPTA bus.

Philadelphia police said Zahkir Whitfield, 15, was on the bus on March 22 when a fight broke out among a group of teens.

Police said 17-year-old Zayki Davis got off the bus and fired a bullet through the window, hitting Whitfield in the chest. Whitfield was pronounced dead at a local hospital.

"I was in shock," Anthony Overstreet, Whitfield's grandfather, said. "It's a tragic thing, but this is where we live at."

Overstreet said Whitfield was a friendly teen who loved playing basketball and swimming. He was a 10th grader at Upper Darby High School.

"I want him to be remembered as a happy-go-lucky kid, free, friendly," Overstreet said. "He would help anybody."

He is demanding an end to the violence.

"I just want to tell the kids to put the guns down," Overstreet said. "Find something else to do. Play your PlayStation, Xbox. Y'all are too young to be losing your lives over nothing."

Police have released images of the four suspects they're looking for. The City of Philadelphia is offering a $20,000 reward for information leading to an arrest and conviction.