Keep in mind that Cho Seung-Hui is the only one responsible for the massacre at Virginia Tech. Nobody else was involved. He was absolutely determined to cause death and pain to those whom he had come to despise, including himself.
So, what would Cho have done if nobody were to have sold him a gun? My thoughts are that he would have gone to the dorm, bludgeoned the woman to death with a legally-purchased hammer or other trauma-inducing “weapon,” and then proceed to engineering classes with a home-made explosive device (again, made with legally purchased materials) and proceed to blow himself and an unknown number of students to kingdom come. After all, the latter method is used almost daily by homicide bombers in the Middle East — why not by Cho as well?
An old, trite expression, “Sly as a Fox” was put to the test by a group of scientists and students in the Pacific Northwest several years ago. They baited and set humane traps in a forested area known to be a Kitt Fox habitat. When a fox was trapped, it was tagged and released. 
Friday, December 15, 2006 marks the 215th anniversary of the ratification of the Bill of Rights, the very essence of our democracy.