Why do the police play 20 questions? Why not show a picture of the gun if they are going to talk about a second "unique" weapon?
Speculation is fun. Impatience for "the answer" is natural (I think).
Maybe the media promised this guy that his family would be rich, in exchange for a captivating story (I doubt it, but you can see how far speculation can go, if one considers news-story to be a motive).
I think he was a victim, not a perp. Based mostly on 1) my prejudice relating to the intelligence of pizza delivery people (good heart, weak mind) and 2) his demeanor.