More than 80% of guns used in mass shootings obtained legally

Handguns are displayed in the sales area of Sandy Springs Gun Club and Range, in Sandy Springs, Ga.
Handguns are displayed in the sales area of Sandy Springs Gun Club and Range, in Sandy Springs, Ga.

The weapons used in this week's massacre in San Bernardino, California, were purchased legally, raising questions about how preventable gun violence is under current U.S. firearm laws.

Eighty-two percent of weapons involved in mass shootings over the last three decades have been bought legally, according to a database compiled by Mother Jones magazine that defines a mass shooting as taking the lives of at least four people in a public place. Using that criteria, Mother Jones found 73 mass shootings since 1982.