All kinds of symbolism with a veterinary kill gun, labeled bullets, and monopoly money. Every part of this seems as if it was meticulously planned out from start to finish by someone(s), and that he has no plans of getting caught. Laughing at the possibility, even. And so far at least it seems that he may very well be right.
Frankly, I'm not sure that one person could conceive of all of the ideological imagery and innuendo unless he is obsessed about the topic, and if he is obsessed by it then it seems there would likely be folks who would suspect him immediately. Unibomber's brother turned him in as soon as he was able to read the manifesto, for example.
And if this was a personal grievance and not an ideological one, it isn't likely that a game would've been employed here. Personal grievers tend to be more passionate about their specific circumstances and want to keep it intimate (i.e. it tends to be about a specific victim and not making some broad ideological statement).
In any case, just more IMO.