The shooting happened just before noon Monday in the 5700 block of Haddington Lane.
The boy was hit in the chest. He was rushed to Lankenau Hospital by police where he was placed in critical condition.
He was pronounced dead at 12:25 p.m.
Police say the boy's brother went door-to-door looking for help after the shooting. A neighbor came to help and the 19-year-old fled the scene, Acting Police Commissioner Christine Coulter said.
However, he was picked up by officers a short time later.
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Coulter said investigators believe the 19-year-old is responsible for the shooting, and they are now investigating whether the shooting was intentional or accidental.
The brothers were the only people inside the home at the time of the shooting.
Coulter said there was no indication the shooting was self-inflicted.
This shooting comes less than a week after a 10-year-old boy was shot in the head while walking home from school. He was hospitalized and is expected to survive. Police are looking for the gunman who opened fire from inside a red Pontiac.
These incidents came just weeks after two shootings that left a 2-year-old girl dead and an 11-month-old toddler fighting for his life.