One of the big questions is what set him off at that time. There had been several major terrorist attacks on concerts and public gatherings at that point, but I can’t think of one particular thing that might have made him move from mathematical speculation to acquiring the weapons.
Also, I am sure he must have had help or had expected to have help in the actual attack.
I too have a very hard time believing he did it all by himself.
I would like to see more evidence before I am convinced that he was the actual shooter, and then killed himself.
If that is the case, I would like law enforcement to describe in detail how they reached that conclusion.