A 53-year-old woman and her 22-year-old son were fatally shot at a Chester County home and their alleged killer then died by suicide, authorities said Thursday.

Pennsylvania State Police and paramedics were called around 1:15 a.m. Wednesday to the 300 block of Ashmun Avenue in Lower Oxford Township for a report of two people in cardiac arrest. Paramedics attempted to resuscitate Kimberly Harris and Jordan Foster before pronouncing them dead at the scene.

The son’s twin brother and a female companion discovered the two victims, who had suffered apparent injuries from a physical assault as well as gunshot wounds. State police investigators found .380-caliber shell casings at the scene.

Investigators later determined that Timothy Harris, 41, allegedly shot the mother and son during a physical altercation, possibly on Tuesday. State police said he had been in a longtime relationship with the mother.

On Tuesday night, Timothy Harris was involved in a vehicle accident in East Marlborough Township, then fled the scene, state police said. Harris then allegedly was involved in a crash in Kennett Township, exited his vehicle, and fatally shot himself with a .380-caliber handgun in front of witnesses.

Chester County District Attorney Deborah Ryan said in a statement: “This is a horrible tragedy that will forever alter the victims’ family, and my sympathy goes out to them. We will use all our investigative resources to discover why this shocking event happened.”

On her Facebook page, Kimberly Harris said she worked as a housekeeping cleaner for Aramark. CBS3 reported that she worked for Aramark at Lincoln University, which is near her home, and that one of her sons was a student there.

A spokesperson for the university could not be reached for comment.