When lights go out and the country sleeps, federal agents work around the clock to stop the flow of illegal drugs and people at the U.S.-Mexico border. It’s an effort that doesn’t always prove successful especially under the cover of darkness.

As the sun sets on the ranch lands of Falfurrias, Texas, night falls with it leaving few sources of light.

The KENS 5 Border Team rode with the U.S. Border Patrol along one of the most trafficked areas by human smugglers and undocumented immigrants along the southern border seeking to make it passed the Falfurrias checkpoint undetected.

The inspection station is located 68 miles north of the Texas-Mexico boundary, in the middle of rural Brooks County.

It’s the last line of Border Patrol defense undocumented immigrants try to bypass before they fall through the cracks of our immigration system.

“In order to go through the checkpoint you are either going to take your dope, your narcotics, or your people through the checkpoint or you’re going to drop them off south of the checkpoint and have them go around the checkpoint to go north,” said Border Patrol agent Pedro Cantu.

Coyotes do this in broad daylight and under the cover of darkness.

“I’m going to pull over and kill the lights just to show you how dark it actually gets out here,” said Cantu as he drove down Texas Highway 281.

Agent Cantu has worked the 1,500 square miles of private ranch land for several years tracking footprints with the aid of night vision technology. Border Patrol calls the process "sign cutting."

Smugglers are familiar with this technique. That’s why they try to erase their tracks to throw agents off their path.

“Their techniques are always evolving always growing. They’re trying to outsmart us,” said Cantu. “So, it’s a cat-and-mouse game on what they can do to not get caught.”

Like chasing a ghost, agents begin to follow the trail of one person’s shoe print.

The caliche terrain can make it difficult for agents to decipher how long ago the person traversed through a certain property.

They were unable to find him.

Fewer and smaller fragmented groups of immigrants complicate the search. A trend that reflects this year’s overall decline in illegal border crossings.

Those are the ones caught. It begs the question: how many sneak through?

“The two parcels that we own, are about 5,000 acres,” said Javier Perez, the owner of La Copa ranch.

La Copa is located a few miles south of the Falfurrias checkpoint.

“People cross here all the time,” Perez noted. “365 days a year, there’s people coming through here.”

Finding a source of water or shelter is nearly impossible around this brush land, reducing the chances of survival if left stranded.

“You can get disoriented very quickly,” warned Perez. “You can get lost, you can get dehydrated, you can be running around in circles and not know where you’re going.”

According to the South Texas Human Rights center, 41 human remains have been found in 2017 in Brooks County. The same organization recorded 61 cases in all of 2016.

The U.S. Border Patrol, on the other hand, has reported 130 deaths in 2016 for the entire Rio Grande Valley sector.

It’s the break of dawn. A border patrol camera sensor is activated.

“As soon as it gets daylight, they [immigrants] can see, ok we need to get in the brush and get some cover,” said agent Cantu.

Agents pick up a trail of a larger group.

“You can see how it’s matted down so, easily 10 plus, maybe 15 [immigrants],” said Cantu as he pointed to footprints.

The fresh prints prompt Cantu to move a couple miles north to cut ahead of the pack.

Time is of the essence. The immigrants have are already walked around the checkpoint.

Border Patrol ATVs are deployed while more patrol units try closing in on the group… but it’s too late.

"Another one bites the dust,” replied Cantu.

The group made it far enough to be picked up by human traffickers and got away.

Coyotes are estimated to have made about $500 per immigrant smuggled.

“We win some, we lose some, but all we got to do is keep trying, right?” said Cantu.

For Cantu and the rest of the agents, it’s back to the starting line. Hoping next time their efforts will pay off.

“It’s the challenges of manpower, infrastructure, and technology that we’re lacking,” he said. “As an agent, we really don’t get discouraged by it, we just have to continue doing what we do and continue our job every day.”

Illegal crossings come in waves and trends. It may rise and fall like day and night and repeat itself again and again.