Seung Hui Cho, obtained his weapons from federally licensed firearms dealers and underwent criminal background checks.
Cho was crazy. Apparently others noticed:
...the shooter at Virginia Tech, also had no history of violence. But he did have a record of mental illness. He frightened people, including his teachers. His behavior worried his roommates enough that they contacted school officials, who arranged a psychological evaluation for him. He was briefly hospitalized, and outpatient mental health treatment was recommended but not required. His parents were never informed. And, as is so often the case, he never followed through in getting help.
Cho was able to buy his gun through the normal channels then spread his carnage on the campus of Virginia Tech. So if the 'loophole' gets closed, the next crazy man will still be able to buy his gun through the normal channels, arrives at the campus of his choice, then tries to top Cho's record.
The closing of gunshows won't stop crazies from shooting people up.