Here's something I found. It's only a summary paragraph, but I'm pretty sure you have to pay to see the whole article, and I'm not going to do that, so this will have to do. It pretty much describes the shooter in the most recent incident.
The "pseudocommando" mass murderer:... [J Am Acad Psychiatry Law. 2010] - PubMed - NCBI
The pseudocommando is a type of mass murderer who kills in public during the daytime, plans his offense well in advance, and comes prepared with a powerful arsenal of weapons. He has no escape planned and expects to be killed during the incident. Research suggests that the pseudocommando is driven by strong feelings of anger and resentment, flowing from beliefs about being persecuted or grossly mistreated. He views himself as carrying out a highly personal agenda of payback. Some mass murderers take special steps to send a final communication to the public or news media; these communications, to date, have received little detailed analysis. An offender's use of language may reveal important data about his state of mind, motivation, and psychopathology. Part I of this article reviews the research on the pseudocommando, as well as the psychology of revenge, with special attention to revenge fantasies. It is argued that revenge fantasies become the last refuge for the pseudocommando's mortally wounded self-esteem and ultimately enable him to commit mass murder-suicide.