The gruesome discovery was made on the 300 block of Ashmun Avenue in Lower Oxford Township.
Pennsylvania State Police say a relative found the bodies of 53-year-old Kimberly Harris and her 22-year-old son, Jordan Foster, early Wednesday morning.
"Like, what happened? Who could have done this?" asked family friend Beverly Velez.
According to detectives, 40-year-old Timothy Harris, Kimberly's boyfriend of 15 years, got into a physical altercation with the pair on Tuesday before he opened fire and killed both victims.
The exact time of the murder is still unclear, but authorities say around 9:44 p.m. that night, state police received a report of a hit-and-run in East Marlborough Township.
Police say Timothy Harris was involved in the crash and fled the scene.
He then crashed into another vehicle around 9:53 p.m. in Kennett Township, police said.
After the second crash, police say Timothy Harris got out of the car and took his own life. It wasn't until after the crash that investigators connected him to the murders.
Police spent Wednesday combing the scene on Ashmun Avenue and talking to residents.
"(Kimberly) came over on Monday and asked me to start her heater for her," recalled neighbor Stanley Gray who was still trying to process the tragedy. "That was the last time I saw her. It's really something. Hard to believe."
Neighbors say Kimberly Harris lived at the home with her twin boys and boyfriend.
One friend says she worked with Kimberly at nearby Lincoln University providing housekeeping services.
The university declined to comment out of respect for the family.
Police say there is no threat to public safety.
The investigation is ongoing.