Central American migrants in Phoenix, Arizona, in 2014. Photo: SAMANTHA SAIS/Corbis

The United States government placed an unknown number of Central American migrant children into the custody of human traffickers after neglecting to run the most basic checks on these so-called “caregivers,” according to a Senate report released on Thursday.

In the fall of 2013, tens of thousands of unaccompanied minors traveled to the U.S. southern border, in flight from poverty and gang violence in Central America. At least six of those children were eventually resettled on an egg farm in Marion, Ohio, where their sponsors forced them to work 12 hours a day under threats of death. Local law enforcement uncovered the operation last year, prompting the Senate’s Permanent Subcommittee on Investigations to open an inquiry into the federal government’s handling of migrants.

“It is intolerable that human trafficking — modern-day slavery — could occur in our own backyard,” Senator Rob Portman, Republican of Ohio and the chairman of the subcommittee, told the New York Times. “But what makes the Marion cases even more alarming is that a U.S. government agency was responsible for delivering some of the victims into the hands of their abusers.”

As detention centers became incapable of housing the massive influx of migrants, the Department of Health and Human Services started placing children into the care of sponsors who would oversee the minors until their bids for refugee status could be reviewed. But in many cases, officials failed to confirm whether the adults volunteering for this task were actually relatives or good Samaritans — and not unscrupulous egg farmers or child molesters. The department performed check-in visits at caretakers’ homes in only 5 percent of cases between 2013 and 2015, according to the report.

The Senate’s investigation built on an Associated Press report that found more than two dozen unaccompanied children were placed in homes where they were sexually abused, starved, or forced into slave labor. HHS claimed that it lacked the funds and authorities that a more rigorous screening process would have required. However, the investigation also found that HHS did not spend all of the money allocated to it for handling the crisis.

The agency placed 90,000 migrant children into sponsor care between 2013 and 2015. Exactly how many of those fell prey to traffickers is unknown, because the agency does not keep track.