All Cops Are Bastards

It was an AD.

AD stands for Accidental Discharge.

This was a negligent discharge. He was negligent by pulling his weapon and having his booger hook on the bang switch while hyped on adrenaline and as a result discharged his firearm and struck an innocent bystander.

This is why you're supposed to be trained to handle firearms so this doesn't happen. But can you imagine cops actually training to do something properly?