I could see a Mosin-Nagant and a WW1-era Mauser, and what appeared to be a sporsterized Mauser, in the photo. These are the types of firearms collected by people with an interest in military history or military firearms, and certainly not the sort one would use in a "shootout with cops".
I shouldn't be surprised, but still am, at the number of people on WS who know nothing about firearms, or firearms collecting. In the part of the country where I live, large gun collections are common. I have one myself.
I think it's because he is a serial killer that's why. A normal person with a gun collection often doesn't alarm anyone.
With him, I'm curious if he only collected guns or used them in crimes or used to threaten women that's all.