“The Santa Barbara shooter had legally purchased and registered firearms”
I don’t think the process was legal. It appears he lied on his 4473 when answering questions about his mental state and mental treatment.
So although he ‘passed’, he lied on his 4473, which is ... against the law.
We need more laws. /$
The 4473 asks nothing of mental treatment. With respect to mental deficiencies, the 4473 specifically asks whether or not the person was adjudicated as mentally deficient (via the court system), or was committed to a mental institution. Neither of which appear to be the case here.