He was not in possession of a firearm when the police entered the apartment, which was after the girlfriend had exited. The police report says nothing regarding whether he had a gun at the time the girlfriend said he did.
I'm not taking a position on what did or did not happen here, but if what you said above is true, where did the gun go? If he barricaded her out of the apartment, and himself inside, and there was no gun found inside the apartment, where did it go (a shotgun, no less)?
I do not know how much time elapsed between the alleged barricade situation and police response, but if it was immediate then it raises other issues.