In order to avoid the checkpoint, many smugglers will drop their migrants off on unmarked county roads, tell them the walk is just a mile or two, and send them on their way with a guide.
The walk is much longer than that, however. Many immigrants wind up walking 15 miles or more through the thick brush and along sand paths that feel heavy beneath their already weary legs.
If they cannot keep up, they are left behind to die of dehydration in the muggy fields. Sometimes, if they refuse to carry the 70-pound packs of marijuana for their smugglers, they are beaten. Women are raped and their undergarments are left hanging in the mesquite trees.
In Brooks County, Texas, the site of one of the checkpoints, 129 bodies were found last year. Already, 33 have been discovered this year.
"This area is the hot spot now," says Linda Vickers, a rancher who has had more than one run-in with the groups and bodies in the area.
The county buries the bodies in the local cemetery and places thin metal signs to mark the graves of the unknown.
"They are humans. That is what we all are," says Benny Martinez, the chief deputy at the Brooks County Sheriff's Department. "Who would blame them for wanting to get out of their country with crime as high as it is. They just want to feel comfortable. They just want to be looked at as human beings."
Back in New York, Luis says he has found it difficult to get law enforcement agents to see his wife as a person worth finding. He says some local police agencies have been slow to investigate and are skeptical of his story. In a world where city, county and federal law enforcement agencies' duties are blurry, he says it's easy to get the run around.
One local law enforcement agent who has worked closely with him, but was not authorized to speak on the record, confirmed that the case fell into ICE's jurisdiction. He also confirmed that his agency had taken down information about Marilu's disappearance and had collected photographs, and passed them along to law enforcement agencies throughout the state.
"It is pretty sad. I am pretty much one of the only [local] agents that takes some kind of report and I send them to Brooks County," he said. Brooks County is the area where many immigrants die of dehydration during their journey.
"When I get calls like this, they are so genuine. I know what is happening. Everyone knows what is happening. We know there is a criminal element that is doing this to the women," the officer said. "You hear countless stories. My wife. My sister. My aunt. My mom. It is sad. God knows how many bodies are out there that have not been recovered yet."
With such a high volume of police reports of lost immigrants, Luis says he has hired a private investigator to help him find his wife.
"Every day I ask God to help me," he says. "Seeing my children is the thing that gets me up every day. I cannot fall. I am a mother and a father to my children now."