Action News has learned the driver of the car and the officer were involved in a dispute.
The off duty officer has been identified as 32-year-old Marc Brady, an eight-year veteran of the police force.
"I was watching TV, and I heard a big bang."
When Lisa Nelson initially ran to her window around 11:30 Sunday night she couldn't see anything outside on the East Mount Airy street. But then she heard sirens.
"The next thing I heard was the paramedics and the fire engine. So I was like, OK something happened," explains Nelson.
Police say Brady had been riding his bike on Musgrave Street by East Meehan Avenue when he was struck by a white Acura. Police say the driver stopped less than a half mile away, but authorities are investigating if the driver intentionally hit him.
The officer was transported to Albert Einstein Medical Center and pronounced dead a short time later.
Police say the driver and the officer knew each other and had been in an ongoing dispute. Detectives believe the pair argued earlier on Sunday.
Police say Brady was assigned to the Differential Response Unit, and was being investigated internally by the Philadelphia Police Department, though the details of that investigation have not been released. Authorities say he had been on desk duty pending the outcome of the investigation.
Neighbors were shocked to hear of another officer losing his life.
Nearby resident Althea Banks says, "You think of the other two that just happened. Almost similar, like bikes, car accident, so it's a shame. It's definitely a shame."
Homicide investigators are conferring with the district attorney's office right now to decide what charges will be filed.