PORT-AU-PRINCE, Haiti - When Walder St. Louis entered the Miami pawnshop in October 2021, his shopping list contained just a few items: Two AK-47s and an AR-15.

Germine Joly, then head of the Haitian gang 400 Mawozo, had placed the order from a Port-au-Prince prison. St. Louis would soon send two barrels of firearms back to the Haitian capital.

Heavily armed gangs control 80 percent of Port-au-Prince, the United Nations has estimated, where they rape, kidnap and kill with impunity. Haiti doesn’t manufacture firearms, and the U.N. prohibits importing them, but that’s no problem for the criminals. When they go shopping, the United States is their gun store. The semiautomatic rifles that have wrought human carnage from an elementary school in Newtown, Conn., to a Walmart in El Paso are also being used to menace the Haitian government and terrorize the population.

U.S. authorities seized some of the guns in the 400 Mawozo plot before they could be smuggled, and Joly, St. Louis and two others pleaded guilty to federal gunrunning conspiracy charges. The gang would soon gain notoriety for kidnapping 17 American and Canadian missionaries.

Other firearms, purchased in part with ransom money, slipped into Haiti undetected. That’s the most common outcome, analysts say, owing to access in the United States, corruption in Haiti and insufficient screening in both countries.

William O’Neill, the U.N.’s independent expert on human rights in Haiti, called conditions here “cataclysmic.” The presidency is vacant; the prime minister has announced his intention to resign; the National Assembly has gone home. Security forces are outgunned by criminals, who have grown in power since the 2021 assassination of President Jovenel Moïse.

O’Neill said last week it was “incredible” that “weapons and bullets are still going to the gangs, mostly from the United States.”

“There’s got to be much, much more vigorous enforcement of the arms embargo by everybody, but certainly the United States,” he said, “because if the gangs don’t have guns or bullets, they lose their power.”

The influx of U.S. guns to criminals is a growing problem across the Caribbean.

Nearly 85 percent of guns found at crime scenes in Haiti and submitted to the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives in 2021, the most recent year for which data was available, were traced to the United States. In the Bahamas in 2022, that figure was 98 percent.

Exasperated Caribbean leaders last year declared the flood of U.S. weapons “a direct threat to our democracy” and urged Washington to join their “war on guns.”

“The right to bear arms is still a raging debate in the United States,” said Philip Davis, prime minister of the Bahamas. “We don’t intend to get involved,” but “their right to bear arms … ought not to give them the right to traffic [them].”

U.S. officials say they’re trying to disrupt what they describe as a relatively new flow.

Anthony Salisbury heads the Miami office of Homeland Security Investigations. Historically, he says, the largest shipments and most powerful weapons trafficked through South Florida have gone to Central and South America.

But in recent years, Salisbury said, authorities have noted a “marked uptick” in the number and size of guns smuggled into Haiti. When they seized .50-caliber sniper rifles, a belt-fed machine gun and a cache of other high-powered weapons bound for Haiti in 2022, he said, “It hit us on the head with a hammer.”

Traffickers are taking advantage of Miami’s “break-bulk” port, a miles-long stretch of the Miami River lined with freighters that carry cargo that’s broken into individual items rather than transported in containers. Haitians in Florida use them to send rice, beans and other supplies home to loved ones.

When the freighters are loaded up, Salisbury said, they resemble a “giant, floating secondhand store” - and are notoriously difficult to search.

“We could get very solid investigative information that there was a load of weapons on a Haitian freighter,” he said. “It would take us weeks to unpack and look for it, and we still may not find it.”

In recent weeks, as gangs set off the worst violence this country has seen in decades, shuttering the airport in Port-au-Prince, busting open prisons and pressuring embattled Prime Minister Ariel Henry to step down, leaders from the United States, Haiti and the Caribbean met to forge a solution.

They announced a “transitional presidential council” to appoint an interim replacement for Henry and lead the country to elections.

But stability is unlikely, sociologist Roberson Édouard says, until the United States works harder to curb arms smuggling.

“Gangs have a destructive and lethal power that relies on infrastructure outside of Haiti,” said Édouard, author of “Violence and the Social Order in Haiti.” “In all the discussions, there is no talk of measures to cut off the sources that fuel the lethal capacity of gangs: Access to weapons and ammunition. That problem comes from the United States.”

By some estimates, there are half a million unauthorized firearms in this country of 11 million, the U.N. Office on Drugs and Crime reported this year. The Haitian National Police in 2015 reported 38,000 authorized weapons.

Some guns arrive in Haiti via the country’s porous land border with the Dominican Republic. The U.N. also identified 11 “clandestine” airstrips here that are “rarely patrolled.”

But many arrive by sea. They’re disassembled into parts and hidden among legitimate cargo, wrapped in aluminum foil or garbage bags, stashed in cars or multi-gallon barrels, buried under clothing or toiletries.

In the hemisphere’s poorest country, heavily dependent on imports, searching all the cargo that arrives is impossible. So is patrolling its 1,100 miles of coastline.

Gilbert Guichard, a divisional coast guard inspector, said the agency has lost about one-quarter of its nearly 220-person workforce to the Biden administration’s humanitarian parole program. Just three of its boats are operational, he said, “and even then, they’re barely functioning.”

Adding to the challenge, some Haitian authorities are in league with the smugglers.

Garry Jean Baptiste, an adviser to the National Syndicate of Haitian Police union, said the understaffed, underequipped coast guard can go months without patrolling the waters. But uncontrolled seas, he warned, “could lead us to catastrophe.”

“The weapons causing insecurity in Haiti are American made,” Jean Baptiste said. “We want to understand why the United States cannot prevent these weapons from entering Haiti, poisoning the lives of the population.”

The arms that are trafficked to Haiti are often purchased by straw purchasers in states such as Florida with permissive gun laws and large Haitian communities. A .50-caliber sniper rifle that sells for $10,000 in the United States can fetch $80,000 in Haiti, Salisbury said.

The Biden administration and Congress agreed in 2022 to increase penalties for straw purchases and firearms trafficking. The Department of Justice last year appointed a coordinator for Caribbean firearms prosecutions.

U.S. and Haitian officials agreed in February to establish a joint investigative unit aimed at boosting the abilities of both countries to prosecute such crimes.

But a Justice Department official said Haitian police are so overwhelmed by the security crisis here that they’re not focused on firearms tracing - a key tool for U.S. investigators. The official spoke on the condition of anonymity to discuss the sensitive issue.

William Kullman, a former deputy chief of international affairs at ATF, visited Haiti before the devastating 2010 earthquake. Even then, he said, the police academy was “dysfunctional.” Some officers collected guns from crime scenes and kept them for themselves because they were so poorly equipped.

“It was very kind of frustrating to try to build up the capacity of the nations to fight weapons trafficking, but at the same time, looking at our own contributions to the problem,” he said. “Even if we just had even minimal export controls, a lot of these things wouldn’t happen.”

Samuel Oakford in Washington contributed to this report.