When a police detective picks up a crime gun and runs a trace, she finds out when the gun was first purchased in a legal sale. If that sale occurred in the previous year, there’s a good chance the firearm was trafficked or purchased with criminal intent.

The aggregate data from those trace reports, analyzed by The Trace, provides a map of the interstate routes that display the most glaring signs of firearms trafficking. The data also bolsters the well-documented pattern of guns flowing from states with loose gun laws to nearby states with stricter ones.

Every year, the Bureau of Alcohol, Tobacco, Firearms and Explosives publishes a cache of reports with facts and figures about gun traces. A trace report is kind of like a Carfax report for a gun, recording the date and location of purchases and the flow from seller to buyer. In addition to looking at the caliber of the weapon traced and where it ended up, the bureau calculates its “time-to-crime,” or the time that has elapsed between a gun’s purchase at a retail location and its recovery during a police investigation.

Experts say a low time-to-crime is one of the best indicators that a weapon was purchased specifically to commit a crime, or to be resold to criminals.

According to the most recent ATF statistics, released in August, the bureau traced 332,101 guns in 2018. The average time-to-crime of those weapons was 8.8 years. That may seem like a long time, but guns — like cars, guitars, and old LPs — are objects that often trade hands. That’s why a particularly short time-to-crime raises red flags for law enforcement, since it often suggests the weapon was acquired for criminal purposes.

Using the ATF data, we identified the states that exported the highest share of recovered guns with a time-to-crime of under one year, a likely indication of trafficking. The states leading the pack include Nevada, Missouri, and Virginia.

The data also allowed us to isolate relationships between states that produce — or are the destination for — a high proportion of low time-to-crime weapons.

Where Out-Of-State Crime Guns Flow the Fastest Source and recovery states with the highest share of guns traced in 2018 with a time-to-crime of under one year. Time-to-crime (TTC) measures the time between a gun’s original sale and its recovery by law enforcement. Source → Recovery Guns Traced % With Short Time-To-Crime Tenn. → Ky. 115 23.5% Nev. → Calif. 1,696 23.2% Ala. → Ill. 131 20.6% Va. → D.C. 596 20.0% Mo. → Kan. 317 19.9% Mo. → Ill. 447 19.2% Ohio → N.Y. 253 18.6% Pa. → N.J. 405 18.0% N.H. → Mass. 184 17.9% Ind. → Ill. 1,531 17.7% Kan. → Mo. 409 17.6% Ga. → N.Y. 574 17.4% Va. → Md. 1,004 16.8% Ga. → N.J. 257 16.3% Iowa → Ill. 172 16.3% Ala. → N.Y. 136 16.2% S.C. → N.C. 687 16.2% Ga. → Ill. 187 16.0% Va. → Pa. 204 15.7% Ga. → Md. 249 15.7%

In California, for example, 12 percent of the guns recovered in the state had a time-to-crime of less than one year. When you isolate only those guns that originated in Nevada and were recovered in California, the figure jumps to 23 percent — almost one in four. (Nationally, 10 percent of all guns had a time-to-crime of less than one year.)

“If that’s not a sign of trafficking, I don’t know what is. That’s really stark,” said Daniel Webster, director of the Center for Gun Policy and Research at Johns Hopkins University.

Webster said the differences between the two states’ gun laws create incentives to traffic weapons across the Sierra Nevadas. California has among the tightest gun regulations in the country, with universal background checks, waiting periods, and limits on certain types of firearms. Nevada, on the other hand, has few regulations on the sale and possession of weapons. A 2017 study published in the Annals of Internal Medicine found that gun shows in Nevada, which until 2016 did not require background checks on private sales made at places like gun shows, were associated with increases in firearm injuries in California.

On the opposite end of the spectrum, states with strict gun laws or that are geographically remote did not export many weapons that were then quickly used in crimes. Of all states, New York exported the lowest proportion of guns with time-to-crime of under one year, followed closely by Rhode Island, Alaska, Massachusetts, California, Wyoming, and New Jersey.

State Exports Of Guns With Short Time-To-Crime 0 4 8 12 16 20 % With Time-To-Crime Below 1 Year Alaska Maine Vt. N.H. Wash. Idaho Mont. N.D. Minn. Ill. Wis. Mich. N.Y. R.I. Mass. Ore. Nev. Wyo. S.D. Iowa Ind. Ohio Pa. N.J. Conn. Calif. Utah Colo. Neb. Mo. Ky. W.Va. Va. Md. Del. Ariz. N.M. Kan. Ark. Tenn. N.C. S.C. Okla. La. Miss. Ala. Ga. Hawaii Texas Fla.

Representatives for the ATF offered differing interpretations of the data. “There is a clear correlation between source areas from where firearms are more accessible and market areas where firearms are less accessible,” said spokesperson Scott Curley in an emailed statement.

But in a second statement, produced in response to follow-up questions, spokesperson April Langwell stressed that differences between gun laws alone do not fully explain trafficking patterns. “Trace and time-to-crime statistics, while clearly relevant, do not tell the whole story. Trafficking patterns involve complex and fluid factors,” she wrote, pointing to population density and the particulars of criminal networks.

Garen Wintemute, director of the Violence Prevention Research Program at the University of California, Davis, also noted that differences in law enforcement policy could affect the data. California, for instance, requires police to submit all recovered weapons for tracing. In many other states, it’s voluntary, and police departments routinely fail to submit weapons to the ATF. That likely results in more data on guns recovered in California than in other jurisdictions, he said.

In California, lawmakers want to coordinate more directly with source states to reduce trafficking. This July, a man committed a mass shooting at the Garlic Festival in Gilroy, California, using an AK-style rifle banned in the state but legally purchased in Nevada. Weeks later, a group of California legislators sent a letter to Nevada Assembly Speaker Jason Frierson, asking him to hold a summit on ways to cut off the interstate flow of weapons. “While California has enacted numerous gun safety measures, this tragedy underscores the need for California to work closely with neighboring states to close loopholes and advance common sense gun safety measures,” the elected officials wrote. The letter resulted in some preliminary discussions between lawmakers from the two states.

Jesse Gabriel, the Democratic assemblymember who wrote the letter, said that ultimately this would be better handled at the federal level: “Part of why you’re getting flows between different states is because you don’t have uniform federal gun laws.”