The sad thing is I think you're serious.
Let me paint a picture for you.
Officer, who ADMITTED he was nervous about the whole situation...goes up undercover to investigate alleged prostitution.
He gets antsy when he runs into some guys who are obviously intoxicated (they were at a bachelor party..) and calls for backup. He follows the guys who still don't know he is a cop. They get worried because they are wasted and being followed by some strange guy. Victims jump into their vehicle and try driving away when the backup shows up and trys to block off the vehicle. Lord knows if there was even ANYTHING that the one victim reached for, testimony just said he reached his hand down or something...Antsy/nervous/shouldn't have a gun in the first place officer calls out "GUN" because he is scared ####-less. He fires multiple shots, deflected bullets fly around thus the other officers think they are being shot at. All officers, but mostly the inexperienced one, shoot at the victim's vehicle. Smoke clears, turns out "hey, there was no gun".
Give me a better story.