In 2007, a total of 12,632 people in the United States were murdered with firearms, and it is estimated that another 48,676 were treated in hospitals for gunshot wounds received in assaults. Guns are frequently used to commit crimes in the United States, partly because they are so easy to get. This ease of access, in turn, is partially attributable to the fact that there are two systems of retail gun commerce in this country, one involving licensed gun retailers and the other based on private-party gun sellers, and only the former of these systems is regulated. Some 85% of all guns used in crimes and then recovered by law-enforcement agencies have been sold at least once by private parties.
Wintemute, Garen J., Anthony A. Braga, and David M. Kennedy. "Private-Party Gun Sales, Regulation, and Public Safety." New England Journal of Medicine (June 30, 2010).