Jake Gyllenhaal witnessed real violence during role research

And the stars got an close-up look at an officer's daily duties when they responded to a call for back-up at an alleged gang shoot-out.

Gyllenhaal and Pena arrived in time to see a paramedic treating a victim who was nursing bullet wounds on his lip and arm.

In video footage, captured by TMZ.com, the two can be seen watching as the injured man was loaded into an ambulance.