With new info it looks like a Marine with PTSD on psychotropic drugs. Everyone of these mass shootings has been psychotropic drugs. It is seriously time to sue the drug companies as the cause of all these events...
It sure bears the FDA doing a black box warning on such drugs when prescribed to males between the ages of 15 and 35.
One class of drugs which seem to show real promise for treating PTSD is psychedelics such as LSD. You can bet that will never get approved.