Supposedly, the killer from Oregon was taking a number of meds for mental illness that can cause violent behavior. Currently in Wisconsin, there are laws that mandate that if you are a schizophrenic or have other mental illnesses, you are reported to a database that prohibits you from being able to purchase a gun. I’m fine with that law, it just isn’t enforced.
http://www.ncsl.org/research/civil-and-criminal-justice/possession-of-a-firearm-by-the-mentally-ill.aspx