MATAMOROS, Mexico (AP) -- Just across the Rio Grande from Brownsville, Texas, stands a dormitory-style shelter filled with people recently deported from the U.S. and other migrants waiting to cross the border.
The long rows of bunk beds offer immigrants a place to rest on their long journey. But the shelter is no safe haven in a town controlled by the Gulf cartel. Armed men once showed up and took away 15 men, who were probably put to work as gunmen, lookouts or human mules hauling bales of marijuana into the United States.
As Congress takes up immigration reform, lawmakers may have to confront the reality of this place and others like it, where people say the current system of immigration enforcement and deportation produces a constant flow of people north and south that provides the cartel with a vulnerable labor pool and steady source of revenue.
"This vicious circle favors organized crime because the migrant is going to pay" for safe passage, said the Rev. Francisco Gallardo, who oversees immigrant-assistance efforts for the Matamoros Catholic diocese.
If Congress sends more resources to the border, the government will also need to account for shifting patterns in immigrant arrests.
The cartel controls who crosses the border and profits from each immigrant by taxing human smugglers. At the shelter, the cartel threat was so alarming that shelter administrators began encouraging immigrants to go into the streets during the day, thinking they would be harder to round up than at the shelter.
There have been record numbers of deportations in recent years and tens of thousands landed in Tamaulipas already this year, the state that borders Texas from Matamoros to Nuevo Laredo. Arizona is often singled out as the busiest border crossing for immigrants entering the U.S., but more and more migrants are being caught in the southernmost tip of Texas, in the Border Patrol's Rio Grande Valley sector.
Apprehension statistics are imperfect measures because they only capture a fraction of the real flow, but the arrest numbers are definitely shifting.
Arrests in the Tucson, Ariz., sector dropped 3 percent last year, while Rio Grande Valley arrests rose 65 percent. In March alone, the Border Patrol made more than 16,000 immigrant arrests in the Rio Grande Valley sector, a 67 percent increase from the same month last year, according to the agency.
Immigrant deaths are also up. The sector reported last month that about 70 bodies were found in the first six months of the fiscal year, more than twice as many as the previous year.
The makeup of the immigrants apprehended here is changing, too, driven by people flowing out of Honduras, Guatemala and El Salvador. The Border Patrol made 94,532 arrests of non-Mexican immigrants along the Southwest border last year, more than double the year before. And nearly half of those came in the Rio Grande Valley sector.
The Border Patrol is responding by redirecting personnel, including sending most new graduates from its academy to the Rio Grande Valley, according to senior Border Patrol officials.
When immigrants from Central America and Mexico arrive in Matamoros ahead of their trip to America, they are met by smugglers who have to pay the cartel tax for every person they take across the border.
Attempts to cross alone are met with violence. Some immigrants are kidnapped and their families extorted by the organization.
Reported murders in Tamaulipas, the state that borders Texas from Matamoros to Nuevo Laredo, increased more than 250 percent in the past four years, according to the Mexican government. Official statistics are generally thought to undercount the real toll. Soldiers recently killed six gunmen in a clash in Matamoros.
And yet, even with the high-degree of danger for immigrants crossing this part of the border, they keep coming.
Central American migrants continue to use the route up the Gulf Coast side of Mexico and through Tamaulipas because it's the shortest to the U.S., said Rodolfo Casillas Ramirez, a professor at Facultad Latinoamericana de Ciencias Sociales in Mexico City. The smugglers choose the route, and even if immigrants have heard about the violence in Tamaulipas, "they trust that the premium they've paid includes the right of passage," he said.
They continue to leave their home countries for economic reasons. Although the U.S. economy has provided fewer jobs for immigrants during the Great Recession and a long, slow recovery, opportunities south of the border have been even more limited, Casillas said.
That's why the Rev. Alejandro Solalinde, a Roman Catholic priest who founded a shelter for immigrants in the southern Mexican state of Oaxaca, said the answer is in regional development, not increased border security.