I have been reading the details on each of the 61 mass shootings that were identified on the Mother Jones website that have taken place in last 30 years (they list 62, but I think classifying the Fort Hood shootings, which were an obvious example of Islamic terrorism, along with the others makes no sense).

There is a very clear and simple pattern of people who feel persecuted and unable to cope with societal pressures. They are usually on the verge of being fired from a job, or have been, or they're being bullied at school, or they are being alienated because they're not originally from the United States (this is an undercurrent in all the Asian shootings, like Virginia Tech, University of Iowa and the Binghamton NY shootings). In almost all cases, they develop a paranoid complex of persecution and see murder as the only way to be free of the persecution (which, of course, they see as the reason for their misery).

Media fame may have played into their actions tangentially, but it does not appear to be a primary or even secondary motivating factor for most of the killers. The primary motivation is that they feel trapped and have nowhere to go.