NYC: Cop shoots cop

I’m not sure what constitutes firearm’s training for NYC's Transit Police, but I’m pretty sure keep your finger off the trigger until ready to shoot and muzzle in a safe direction are in the curriculum. Since shooting a pistol requires a finger on a trigger and the conscious decision to press the trigger I’d say this wasn’t accidental in any sense of how most of us define the word. Methinks the word you’re looking for is negligent.