My two main issues are. Was there an apparent motive other than conducting official duties? Did he have a legal right to keep the firearm(s) after taking possession of it/them?
Spin me out a hypothetical where they call the police to come pick up a gun, various police call each other to send a guy out there, the guy goes out there because the police were called and he was the police officer who does that sort of thing, the guy takes possession of the gun, as a police officer,, runs checks on it....and the gun is never checked in to evidence....and yet he is not conducting official duties or had a legal right to keep the gun.
I'm game.