I am sorry, but the only bearing I could see the economy having on the types of shootings we are discussing would be if we were to have an economic boom, and suddenly put much more funding into mental health care.
Columbine, Aurora, Tucson, Newtown, Virginia Tech, Clackamas - none of these were by poor or indigent people. These atrocities were committed by people who were known to families or co-workers as having mental health issues prior to their crimes.
In those cases where proper diagnoses had not been made, there were plenty of warning signs.
This is not about the economy. That may drive robbery rates, or suicide rates, but it does not drive this type of crime.