Those fires were set in the span of an hour in four different police districts early Monday morning.
Gwendolyn Bonaparte walked by one of them on her way to work.
READ MORE: Philadelphia police investigate fires intentionally set to police vehicles across city early Monday
Bonaparte exclaimed, "Oh goodness- that's bad. That's real bad. People that help us- come on- why would somebody do that?"
Investigators say the arsonist launched a Molotov cocktail into the police cars to set them ablaze.
"Throughout the night we worked very hard to make sure we cover down for the safety and security of our vehicles, and obviously the officers who were assigned to those vehicles," said Philadelphia Police Commissioner Danielle Outlaw. "We get up to serve complete strangers, folks that we don't even know. And to damage the tools, one of the tools that we have available to us, to not only keep us safe, but in order to allow us to do our job, it's a real slap in the face."
No officers were injured.
If you have information, you can call 215-686-TIPS, or 911.