Now, addressing the state law that permits him to buy one at all is a good start. But, the flaw isn't with the process but with what gun sellers have access to.
Even if Cho had been diagnosed with some psychosis that would have normally precluded a person from having a gun, unless he committed some crime that would have flagged him on the background, the result would have been the same.
Sounds like your beef is with HIPA. Unless you're suggesting that guns be banned altogether and that's a whole 'nother argument.