Christopher was shot in the chest and rushed to the Hospital of the University of Pennsylvania, where doctors were unable to save him.
"At 13 years old, he's just a baby," said a neighbor who identified herself as Ms. Diggs.
Police said that .45-caliber shell casings littered the living room and that they found a large amount of narcotics inside.
Investigators said the house is known to police for drug activity, but police were unsure whether the boys were the intended targets.
About 9 p.m., Commissioner Charles Ramsey and other police officials stood outside the house as neighbors lined the block. A group stood sobbing beneath the orange glow of a streetlight, their anguished cries drowned out by the thrumming helicopter overhead.
An 18-year-old man who was a family friend and the boys' 40-year-old father were in the house at the time of the shooting and were taken to speak with homicide detectives, police said, but no arrests had been made as of Wednesday morning.
By 10:30 p.m., a group of neighbors had joined hands and bowed their heads, praying for guidance for young people and comfort for the family and friends of the two young men, the latest victims of gun violence in Philadelphia. According to Police Department statistics, the slayings were the 200th and 201st homicides of 2012.
Diggs said that in her six years in Overbrook Park, she's never seen the type of violence that unfolded on Westbury Drive Tuesday night.
"When you wake up in the morning, you don't expect to see your last day," she said, adding that the city's relentless violence has cheapened the impact of each life lost. "Years ago it was news — it made the front page. And now it's an everyday occurrence. It's always sad and disappointing, though."
Another neighbor summed up the block's attitude: "This block is like family. I'm very saddened by this whole thing."
Contact Phillip Lucas at 215-854-5914 or firstname.lastname@example.org. Follow him on Twitter @UnPhiltered and read his blog, PhillyConfidential.com .