The reward, offered by the U.S. Marshal's service, was announced at a news conference on Tuesday.
District Attorney Mike Green said he hoped the money would help entice someone to come forward with the information needed to get a killer off the streets.
"When we have identified those responsible we intend to vigorously prosecute those people for taking the innocent life of Terrence Webster," Green said.
The shooting happened at an apartment complex in the 1200 block of West Ninth Street around 2:30 Saturday morning. Police say the family had just gotten home when someone opened fire.
Terrence Webster was shot in the head. His mother, Tisheta Green, 25, was shot in the left leg and his father, Thomas Webster, 26, was shot in the left hand.
Terrence died on Monday due to his injuries. Both parents were treated for their injuries and released.
Anyone with information can call the Chester Police Crime hotline at 610-447-7810 or the Delaware County Criminal Investigation Division at 610-496-4359. Tips can be made anonymously.
