Top Democrats on both the House foreign affairs and judiciary committees called Thursday for an inquiry into Drug Enforcement Administration-led operations in Honduras and Mexico that resulted in the deaths of dozens, possibly hundreds, of people who had nothing to do with the drug trade.

The letter, addressed to Attorney General Jeff Sessions and Secretary of State Rex Tillerson, drew on a scathing Justice Department inspector general investigation into a 2012 DEA operation in Honduras — known as “Operation Anvil” — that had targeted drug trafficking networks operating along that country’s Caribbean coast. During one botched operation, members of the agency’s vetted Honduran federal police unit — acting on the DEA’s orders — fired on a water taxi carrying people who were apparently unarmed and not connected to the drug trade. Four people were killed and another four were injured.

The letter also refers to a ProPublica investigation into a 2011 massacre by the Zetas cartel in the Mexican state of Coahuila that was triggered after sensitive information shared by the DEA with its Mexican vetted police unit wound up in the hands of cartel leaders, who ordered a wave of retaliation against suspected traitors.

The massacre left dozens and potentially hundreds of people dead and missing in and around a small, quiet ranching town called Allende, which is a 40-minute drive from the Texas border. The story was published in partnership with National Geographic in June.

“We believe these and other troubling issues merit further inquiry,” read the letter, written by Rep. Henry C. “Hank” Johnson, Jr., of Georgia, and signed by Rep. John Conyers of Michigan, the ranking member of the judiciary committee, New York Rep. Eliot Engel, the ranking member of the foreign affairs committee, and 11 other representatives.

“Given that both the (IG) review and a recent ProPublica report have revealed deficiencies in U.S.-vetted police units in Honduras and Mexico, are you carrying out a thorough review of our government’s system of vetted units to ensure that improvements are made?” Johnson asked in the letter.

For two decades, the so-called “Sensitive Investigative Unit Program” has been the DEA’s workaround method of battling drugs with a foreign partner it doesn’t trust. The agency sets up a unit under its supervision, culling members from the host country’s police forces. Then it trains these foreign officers — often in the U.S. — polygraphs them, and, in some cases, works alongside them in the field.

The agency has established SIUs in some 13 countries around the world. Administrators at the agency have hailed them as the “bread and butter” of the DEA’s activities abroad.

In Mexico, however, the SIU has been plagued by corruption from the start. Since 2000, at least two supervisors have been assassinated after their identities and locations were leaked to drug traffickers by SIU members, according to allegations by current and former DEA agents who worked in Mexico. Earlier this year, another SIU supervisor, Ivan Reyes Azarte, flew to Chicago and surrendered to U.S. authorities who charged him with collaborating with drug traffickers.

The DEA doesn’t dispute the corruption within their Mexican unit’s ranks. In interviews, several agents said that part of “the game” of working in Mexico involves understanding that the vetted unit — and every other Mexican law enforcement agency — might leak to a specific cartel and reliably help pursue another. The trick, they said, was figuring out which cartel the vetted unit was helping, and then using the unit to pursue that cartel’s rivals.

But the investigations by ProPublica and the inspector general made clear that sometimes there are tragic consequences to the game. And while the DEA is quick to take credit for the times it helps its foreign partners capture drug cartel kingpins, it remains silent or claims innocence when lives are lost as a result of its operations.

In the case of the Mexican massacre, DEA officials failed to conduct an internal review of the agency’s role in the attack, and did not either suspend its relationship with the vetted unit or offer to provide assistance to those victimized by the leak. And in Honduras, Inspector General Michael E. Horowitz found that the DEA not only failed to conduct a review of the gunfight, but knowingly misled Congress in an attempt to cover up its role.

Among the revelations in the IG’s report: DEA and state department officials told Congress that their Honduran law enforcement partners fired on a water taxi because passengers on the taxi had fired first, but there was “no credible evidence that the individuals in the passenger boat fired first.” Available evidence “places into serious question whether there was gunfire from the passenger boat at any time,” the report said.

Although the DEA has insisted that it played only a supporting role in the Honduran operation, the inspector general found that it was a DEA agent who ordered a helicopter gunner to open fire on the water taxi.

In a press release, Johnson wrote that the IG report “confirms our worst fears,” and leaves many questions unanswered. “The biggest question of all is: what is our government doing to fix this and make sure that, going forward, any U.S. agent involved in the loss of innocent life abroad is held accountable?”