This May, a public bus was traveling its usual midday route between the San Salvador airport and the city when a few men hopped on board, wearing the uniforms of road maintenance workers. Then they pulled out assault weapons and started firing on the passengers. Their targets were apparently two prison guards and a police investigator who were on the bus at the time, but three others were also mowed down in the attack. To Harry Penate, an adviser for the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) who is based in the region, the incident was horrifying, but not remotely remarkable. “There’s examples like that every day on the news,” he explained, mentioning a week in early July when warring gangs were responsible for not one but two grenade attacks on the outskirts of Guatemala City.

Penate, a Cuban-American from New York City’s Hell’s Kitchen, is the ATF’s only agent for all of Central America. From his desk at the U.S. Embassy in San Salvador, he is the one responsible for tracing U.S. guns smuggled into the Northern Triangle: El Salvador, Guatemala, and Honduras. That role has given him a front-row seat to a bloodbath. Looking beyond the region’s homicide rates, which are some of the world’s highest, what stands out is the number of gun homicides. And since Penate took on the job two years ago, he has come to an inescapable conclusion: U.S. weapons are partly to blame for the carnage—and in turn for the kids who are fleeing it. “I feel as bad about guns going into Central America and Mexico as good, hard-working Colombians feel about cocaine going into the U.S.,” he says.

By the ATF’s count, more than a third of the traceable guns seized from criminals last year in the Northern Triangle that originated from the United States were purchased from a retail dealer. The weapons are then smuggled south in cars and trucks, or in checked airline luggage, air freight, or even boats. That may sound like a lot of effort, but buying from U.S. gun stores is a lot more convenient for gang members. Thanks to our lax gun laws, there is little official paper trail, and the weapons (Northern Triangle gangs favor semi-automatic pistols) are cheaper than buying locally. “It’s a lot easier for me to go to a gun store in the U.S., buy a Glock, and ship it in parts in a microwave oven and have it show up at a relative’s house,” Penate says. He’d recently helped trace a gun recovered in El Salvador that had been purchased only six days earlier from a licensed dealer near Baltimore. When the “time-to-crime” is that short, he explained, the gun was probably “specifically purchased to be trafficked.” And just this month, an Indianapolis man was sentenced to 39 months in federal prison after he admitted to buying 28 handguns for shipment to Honduras, some of them tucked inside a plastic three-drawer CD organizer.

The flow of guns is critical to the gangs’ chokehold over the Northern Triangle. The most powerful gangs, MS-13 and 18th Street, are building ties with the cartels that traffic drugs to the United States through Central America. But their basic operations are fueled by rampant gun-related crime at the local level. “The firearm is to a gang member what a hammer is to a carpenter,” Penate says. “You have a lot of people unemployed who join gangs for protection, and you have everyone getting extorted, from the pupusa vendor on the corner to mom-and-pop businesses to bus drivers.”

For his part, Penate is doing his best to combat the problem. He has persuaded authorities throughout the region to get their forensic labs to submit crime guns to the ATF’s online tracing system. He trains local prosecutors and police to build stronger cases in gun crimes. But he’s largely on his own, with just a few local hires, until he gets a long-awaited deputy later this year—and the ATF hasn’t been inclined to devote more resources to international gun-trafficking. The agency recently shut down its Colombian office and declined to accept an offer of several million dollars from the State Department to expand its anti-trafficking operations in the Caribbean. And in July, when the White House invited relevant agencies to submit requests for emergency funding to help deal with the migrant surge, the ATF did not seek any of the money—an abstemiousness one rarely encounters in the federal bureaucracy. “The focus of the request is the surge of migrants crossing the U.S. border,” the agency said in a statement. “ATF’s role is limited in that regard.”