There is only one underlying trait that all these shooters share, and that's a serious mental instability.
No amount of gun laws will address that unless you tailor a law that specifically targets mental capacity in some way.
The obvious course of action would be to have medical professionals in the field get together and try to formulate some type of plan to tackle mental illness in a serious fashion.
Short of changing the Constitution to ban guns you will never stop random violence and even then it would be futile as evidenced by all the criminals who have guns despite it being illegal.
We don't ban cars because of drunk drivers. We don't ban mini skirts because of rapists. We force drunk drivers into treatment. We jail rapists.
Why not treat seriously the mental illnesses that lead to tragedies like this? Further gun restrictions will not cure the illness that led to this outcome.
The problem is that the mental health industry has devolved to the point to where they only have one answer to all mental health problems...drugs for the rest of your life. I watched these quacks nearly destroy my son with drugs...I managed to rescue him only to lose him into their clutches again...which ended up with him taking his own life.
If some of these folks think the NRA is big and powerful...they ain't but a pimple of the ass of Big Pharma.
If someone wants to do a study that might shed some light on the causes of some of these mass shootings, they outta look into what kind of drugs these people were on or not on.