<<We're not talking about "Joe Public" - we're talking about someone who wants to commit mass deaths. That someone would have practiced.>>
You're assuming the guy would have the same appreciation of the value of practice as you do. It's an invalid assumption, considering that if he were inclined to commit mass murder, he would not necessarily be functioning with a full deck and might figure all he needs to do is to upgrade the arsenal. You're entitled to make whatever assumptions you like, but don't expect the police, whose lives are on the line, to follow you through all your twistings and rationalizations. For the police, what the guy's boss told them (and I'm reasonably sure that they don't just lap up and swallow whatever their informants or complainants tell them, with zero witness evaluation skill) including or with the addition of: the weapons upgrades, the recent lay-off, the "very disgruntled" comments all added up to: "Let's not just walk up the front walk and ring the doorbell."
You and Prince can second-guess them with your silly nit-picking till the cows come home, but I'm reasonably certain they did the right thing and there's a reasonably good possibility that they are all (including the subject of the investigation) alive today because of it.
