How guns move across the country.

By Philip Bump @ WashingtonPost.com, July 31

The rifle used to kill three people at a food festival in Gilroy, Calif., on Sunday was not legal to own in that state. The man police have accused as the gunman apparently evaded security by cutting through a fence to enter the venue. To obtain the weapon, he did much the same thing, purchasing it from a retailer in Nevada, where buying and selling the model that was used doesn’t violate the law.

This is not uncommon. Particularly in states where gun laws are more strict, firearms recovered by law enforcement are often found to have originated in other states. For example, several years ago, we looked at data on firearms recovered in Chicago. About a fifth of those weapons were purchased in nearby Indiana.

The Bureau of Alcohol, Tobacco, Firearms and Explosives collects annual data on the points of origin of firearms recovered in every state [....]