An investigation by four veteran Reuters reporters finds a link between the Biden administration’s use of an app that makes asylum seekers wait for weeks in Mexico, and an increase in attacks on migrants, especially rapes of migrant women, in Mexico’s organized crime-dominated northern border state of Tamaulipas.

U.S. President Joe Biden’s administration in May moved to a new system that required migrants to secure an appointment—via an app known as CBP One—to present themselves at a legal border crossing to enter the United States.

Nine experts, including lawyers, medical professionals, and aid workers, told Reuters the new system has had unintended consequences in the two cities, contributing to a spike in violence.

The high risk of kidnapping and sexual assault in Reynosa and Matamoros is one of the factors pushing migrants to cross illegally, four advocates said. Crossings border-wide surged in September.

Tamaulipas border cities like Matamoros and Reynosa have been notoriously dangerous for years. They’re home to the decades-old Gulf Cartel, the Northeast Cartel (an heir of the Zetas), and other splinter groups that compete violently.

These regional cartels have less-solid control of their territory than do larger national cartels like Sinaloa. This makes them more prone to use violence against newcomers and outsiders—including U.S. citizens, four of whom were kidnapped, two killed, in March when they came to Matamoros for a cosmetic surgery procedure. These criminal groups also make somewhat less money from the drug trade than the larger cartels; such “poorer” criminal groups are more likely to fund themselves by preying on vulnerable people, including migrants.

The Mexican state, especially the hyper-corrupt local government in Tamaulipas, is no protection. Officials often collude with organized crime.

So in recent months, when an asylum seeker uses CBP One, they can travel from elsewhere in Mexico to the border and show up at a U.S. port of entry at their appointed time. They do not need to hire a smuggler. That’s great.

What’s less great is that, when the port of entry is in south Texas (Laredo, McAllen-Hidalgo, and Brownsville, which make up 42 percent of CBP One appointments border-wide—605 out of 1,450 daily spots), the asylum seeker must travel through Tamaulipas territory under organized crime control. In order to be sure not to miss their appointment, they may even stay in this territory, near the port of entry, for days or weeks.

When they do that, the cartels—whose eyes and ears in the region are thorough enough to rival Cold-War East Germany—often find them and demand money. Reuters explains:

[C]riminal groups are still demanding these migrants pay to enter their territory, the experts said.

“Rape is part of the torture process to get the money,” said Bertha Bermúdez Tapia, a sociologist at New Mexico State University researching the impacts of Biden’s policy on migrants in Tamaulipas.