'Rampage' scene in the film

Have just seen this film after missing it for years.
Enjoyed it greatly. Excellent film.

I have one question though (which Philly people here can help me with): was the rampage scene near the end of the film extreme poetic licence, or did Philly cops actually go on a brutal rampage?. That scene shocked me, and I am both fascinated and horrified to find out the actual truth of the scene.