I agree with much of what you've said, Open. And, it is true, many of these mass killers either commit suicide or are taken out at the scene of their crimes.
Regarding the family, they don't appear to have been "without money." The picture of the house in which the mother and son lived was more like an exclusive estate, it doesn't appear money would have been an issue.
I also have concerns about the mother and her love of guns. She had these assault weapons in the house, knowing she had a very sick young man in her charge.