April 16 marked five years since the massacre at Virginia Tech, where a mentally ill student, Seung Hui Cho, used two handguns he had bought legally to kill 32 people and wound 25 others.

Other than a relatively minor law to improve the U.S. national database used for background checks, no significant gun-control legislation followed that tragedy.

Since then, there have been several mass shootings, including additional school rampages and the attempted assassination last year of Democratic U.S. Rep. Gabrielle Giffords of Arizona.