Personally I think the two are definitely related and that there was a major issue that had been brewing for months. Maybe all he did want were friends but nobody would give him the chance because he was misunderstood and then one day he had enough of being invisible and decided to commit the henious crime.
It reminds me of the Elliott case which i won't go into too much detail on (personal connection) but in that case, Weatherston was committing a revenge based murder.
Also, had he been homocidal since he was a child? Did he torture animals? Did he scare women? Why hadn't he had a girlfriend?
Why did he refer to himself as the joker? The villian/hero complex raises something interesting. I was thinking about it, did he consider his quiet self to be batman and this side the joker? Was he bipolar in personality? Or did he have other personalities too?
Why didn't the gun range person report him?