The burglar known as "white boy" cut a hole in the roof of a Virginia gun store last July and took 40 weapons.
Within a month, some of those guns began showing up on the streets of Baltimore - 100 miles from the tiny Shenandoah Valley town of Washington, Va. Police seized the first on West Lombard Street in August. A suspect fleeing from police tossed away another on Hollins Street in September.
A third gun from that burglary garnered the most attention - a West Baltimore gang member used it in a series of daylight gunfights with police in April. One officer was struck in the thigh; the suspect is recovering under guard in a hospital.
"Most of those guns on the street are stolen from somewhere," said Sgt. Richard A. Willard, a supervisor in Baltimore's police gun task force. "These guys need an outlet to sell their guns."
And many of these weapons are imported from Virginia and other states.
A new analysis of violence in Baltimore by the Bureau of Alcohol, Tobacco, Firearms and Explosives shows that trend: 44 percent of the guns used in Maryland crimes last year came from over the state line. That makes Maryland one of the largest importers of guns that are recovered by police at crime scenes, according to the Brady Center to Prevent Gun Violence.
Experts said Maryland's tough gun control laws likely explain why so many of those guns come from elsewhere.
"Maryland is doing a pretty good job. It is making it much harder for criminals to get guns," said Daniel Vice, senior attorney at the Brady Center.
Only seven states, plus the District of Columbia and the U.S Virgin Islands, import more guns, according to the center's data.
Vice said he hopes that data will help persuade lawmakers that tighter gun regulations work, but other researchers in the field don't think that will happen.
Jens O. Ludwig, a University of Chicago professor who studies illegal gun markets, doubts that new federal laws will be passed. So, he says he thinks policymakers need to focus on enforcement rather than legislation.
"The state borders are porous," Ludwig said. "It is hard to regulate your way out of it. You are an island of tight gun control in an ocean of lax laws."
But local authorities say that building cases across state borders presents enormous challenges. Coordination is needed between multiple law enforcement agencies, and Congress has created barriers that prevent individual cities such as Baltimore from seeing federal data about problem gun stores or individuals.
Meanwhile, law enforcement agents say gun traffickers tend to run small operations, creating further challenges.
"There is not one big warehouse in Tennessee that we can shut down and solve the problem," said U.S. Attorney Rod J. Rosenstein. "They are coming from a lot of small sources."
Also, the people who buy and sell guns on the illicit market tend to be sophisticated and hard to catch, said Daniel Webster, a co-director of the Johns Hopkins Center for Gun Policy and Research. His work has shown that there is broad awareness among criminals that police do ballistic traces on weapons, which makes them reluctant to purchase a used gun or buy from anyone they don't trust. "The thought that runs through their mind is, 'Where has that gun been?'" he said.
Webster has been advising Baltimore's Police Department to focus on suppressing demand for weapons. "The most cost-effective way of reducing gun violence is to focus on illegal possession of guns and making that a very risky thing to do," he said.
Baltimore police have been pursuing that approach, particularly in the past year under the city's new commissioner. Officers from specialized units have flooded the high-crime Eastern and Western districts with instructions to look for known criminals with guns. This year, the murder and shooting rates have fallen by 30 percent citywide. Much of the gain comes from a steep decline in murders in the Eastern and Western districts.
But city officials say that the efforts to go after suppliers are worthwhile, too.
"If almost half of our crime guns is coming from outside of the state, we need to be able to see who the main culprits are," said Sheryl Goldstein, the head of the Mayor's Office of Criminal Justice. "We need to be able to work with our regional partners to combat that."
A comparison of the sources of guns used in crimes shows that Maryland and New York have eight of the top 10 states in common, so Goldstein is working with her counterpart in New York City to build a database so that police departments in both cities can share data about guns they recover. She hopes that other cities in the region will link into the database, enabling detectives to mine for patterns about the origins of illegal guns.
Maryland's top supplier states last year were Virginia, North Carolina and Pennsylvania.