One brother said Stephen had no interest in guns....but I think this same brother said...."he had a couple handguns...but he kept them in a safe"....and I think this same brother said that Uncle Steve took his kids skeet shooting.
One of my friends was a professional shooter. He had a safe (Wells Frago) in his basement for his prized possessions.
The killer had a safe in his garage, the size of a refrigerator, according to a neighbor. Now you need a mover for that....check local movers....there's a safe someplace. Did the killer have a storage locker someplace?
Gun safes, even big ones, are not all that hard to move.
You are right .
The family and the girl friend or whatever she was know .
The family? They knew the guy was strange, but was there really enough contact between them that they'd have an inkling that he was planning something?
Politics? I think he wanted a big scene. He wanted to kill as many people as possible. He might have hit on an ideology that would justify that in his own mind, but politics or ideology may not have been his primary motive.