Expert Commentary

How state policy affects how guns move between states

2013 study from Brown University traces guns recovered from crime scenes back to the states where they originally were sold by gun dealers.

The December 2015 mass shooting at a holiday party in San Bernardino, Calif. raised questions about how the two suspects acquired their assault-style rifles. California, which has some of the strictest gun-control laws in the country, prohibits assault weapons with magazines that detach for quick reloading. Law-enforcement officials eventually confirmed that the rifles were purchased legally but noted that they were illegally modified to make them more powerful.

The renewed debate on assault rifles since the attack has focused in part on how easy or difficult it is to move guns across different states. A study written for the National Bureau of Economic Research that was published in 2013 in the American Economic Journal takes a close look at this issue. In “State Gun Policy and Cross-State Externalities: Evidence from Crime Gun Tracing,” Brian Knight of Brown University used 2009 data collected by the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) to trace guns recovered from crime scenes back to the states where they originally were sold by gun dealers. Knight analyzed the movement of 145,321 traced guns. He also investigated the gun regulations of individual states.

Key findings include:

  • About one-third of the guns found at crime scenes had been purchased in different states.
  • Southern states and Mountain states tended to have weaker gun laws.  States in the upper Midwest and along both coasts tended to have stringent ones.
  • In some cases, the strength of gun laws varied substantially among neighboring states. For example, Illinois had “relatively strict regulations” but the states that bordered it – Indiana, Kentucky, Missouri and Wisconsin – had “relatively weak regulations.”
  • Gun-trafficking flows are connected to gun regulations. Guns are often transported from states with weak regulations into states with strict regulations.
  • Guns move more often between nearby states than between two states that are far apart.

The author notes that his findings have numerous policy implications for a nation in which gun policy is largely decentralized. As of 1999, there were a total of about 300 state laws related to guns.

Related research: A 2015 report published in the American Journal of Public Health, “State Firearm Legislation and Nonfatal Firearm Injuries,” examines whether stricter state laws are associated with fewer non-fatal gun injuries. A 2009 study published in the Journal of Urban Health, “Effects of State-Level Firearm Seller Accountability Policies on Firearm Trafficking,” explores the relationship between restrictive gun-purchase laws and gun trafficking.  A 2009 study in Criminology and Criminal Justice, “The Illicit Firearms Trade in North America,” looks at gun misuse and the sources of crime guns in the United States, Canada and Mexico.


Keywords: gun trafficking, gun laws, weapons, assault rifle, firearms