A new study on guns that were seized by Chicago police shows that suburban gun shops are a main source of guns used in crimes within the city, according to an article from the Chicago Tribune.

The research shows that roughly 29 percent of guns recovered in Chicago between 2008 and the end of March 2012 were bought in Cook County suburbs. Lake County, Ind., was the second largest source – accounting for six percent of the weapons – and other counties surrounding Chicago, including Lake County, Ill., and Will, DuPage and Kane counties, the article states.

Two gun stores in suburban Lyons and Riverdale accounted for more than 10 percent of the guns recovered, according to the Tribune.

The study covers 17,230 guns that the federal Bureau of Alcohol, Tobacco, Firearms and Explosives successfully traced after they were recovered in Chicago. Many of the guns couldn’t be traced due to their age or other factors. The University of Chicago Crime Lab analyzed the data.

Police are searching for a solution to the gun violence plaguing Chicago, and the numbers help investigators identify the paths that guns take from being sold legally to being carried illegally or used in crimes, says Roseanna Ander, the lab’s executive director, in the article.

The numbers don’t necessarily mean that the gun stores are violating any rules, as guns are often stolen from their legal owners or bought by “straw purchasers” who pass them to criminals who would be prohibited from buying firearms, Ander says in the Tribune article.

She also says that she was surprised at the percentage of guns that came from Illinois, rather than neighboring states with comparatively relaxed gun laws.

About 42 percent of the guns came from Illinois, while Indiana contributed 18 percent and Wisconsin accounted for 4 percent of the firearms, the article says.