Editor's note: This story contains descriptions and photos of human remains that some readers may find disturbing.

Border Patrol agents steer their all-terrain buggy through dense brush on the historic King Ranch. They're looking for a human skeleton.

They spotted bones earlier in the day when they were chasing a group of migrants through this pasture, and they marked the GPS coordinates. Now they're returning with a sheriff's deputy.

Then they find the remains, next to a patch of orange wildflowers, in the shade of a mesquite tree. The bones have been scattered asunder — some vertebrae, part of the pelvis, the jaw.

"The animals get to them, and they just tear 'em apart," says Deputy Bianca Mora with the Brooks County Sheriff's Office.

The discovery of the bones this month is a grim reminder of an aspect of illegal immigration that is often overlooked these days, with the Trump administration focused on the U.S.-Mexico border, where thousands of migrants are crossing every day.

The reality is that not all migrants headed north are apprehended or turn themselves in to ask for asylum. Some try to evade capture, hiking through sweltering ranch country to avoid federal agents. And some don't survive, especially as temperatures soar into the triple digits during summer months.

The government recorded 283 migrant deaths along the Southwest border last year, compared with 471 in 2012. While the numbers are trending down, the bodies keep turning up. And it's impossible to know how many more migrants are attempting the dangerous trek these days.

In Brooks County alone — about 70 miles north of the border — the sheriff's office has recovered nine sets of human remains this year. That brings the total to nearly 650 bodies found here over the past 10 years.

This is where a long process begins — to identify the remains and, if they are those of a migrant, to find the relatives and send the remains to the migrant's home country.

To that end, Mora gathers up the bones on the King Ranch, along with other items found in the clearing: a blue shirt, a pair of jeans and a weathered cellphone.

She zips them into a white body bag, slings it over her shoulder and heads back to the bush buggy.

This is no country for old or young men, with its sandy ground, spiny plants and punishing sun.

And some migrants succumb to dehydration — an awful death. First come leg cramps and headache, then dizziness, delirium and, finally, unconsciousness, as low blood pressure disables organs.

"They're not equipped for the walk. They don't bring enough water," says Brooks County Sheriff Benny Martinez. "If for some reason they get hurt or they get sick, they're gonna be left behind because the smuggler is on a timeline to get them to a certain location to get picked up further north."

Brooks County is situated on a major human smuggling route that goes from the Rio Grande to the interior of the United States. Coyotes and their migrant clients slog through these vast cattle ranches for days to avoid a busy Border Patrol checkpoint on U.S. 281.

Martinez fights the urge to regard recovering the bodies as routine.

"What we don't want to do, what I don't want to do, is desensitize myself from this," he says. "They are humans. They belong to someone."

Who do they belong to?

Remains are identified in a discreet laboratory in the hill country southwest of Austin that's part of Texas State University.

It is here where they seek the story of the bones.

The project is called Operation Identification. They take in remains that are believed to be those of migrants and that are found in the Texas borderlands or are exhumed from unmarked graves. In a white-tiled lab, they seek to identify and repatriate the bodies, using the latest forensic science.

On a recent trip there, skeletons repose on steel tables. An air exchanger filters the potent odors. Intense graduate students in gloves and blue biohazard smocks are preparing for an intake.

"The zipper might be broken. You can probably break it along the zipper," says Chloe McDaniel, the lab manager. "Also, it might splatter."

She oversees the cutting open of a black body bag that has hardened over time. This is not the migrant found by the Border Patrol on the King Ranch. This individual was found somewhere else in rural Brooks County in 2005. He was buried in Sacred Heart Cemetery in the county seat of Falfurrias.

"Unknown male. 2-21-05. Howard-Williams Funeral Home," a student calls out to the note taker.

The body is in an advanced state of decomposition. After 14 years in a plastic bag, the tissue is the consistency of wet clay, and unrecognizable.

The student volunteers are detectives who practice forensic anthropology. They analyze skeletons to determine age, gender, height and physical abnormalities, in the hopes of making a positive identification.

"About a year and a half before I applied for this program, my dad passed away. My family knew what happened to him," says Courtney Siegert, a 30-year-old doctoral research assistant who works in the lab. She chokes up with emotion.

"When I heard about this project, realizing other people don't get the same kind of answers that my family and I got, I had to be a part of that."

The students carefully extract all the bones from the human remains and deposit them in a big steam-cleaning kettle to be sanitized.

"Once the skeleton is cleaned, we'll do a full anthropological analysis and submit DNA," says Siegert.

At the end of the process, everything they've learned about the migrant is sent to NamUs, the National Missing and Unidentified Persons System. It's a searchable database located at the University of North Texas.

Identification is challenging. Since the program began in 2013, it has taken in 287 individuals and made only 31 positive identifications. Most of the remains they have analyzed came from the Catholic cemetery in Brooks County.

"When an individual dies, their chances of being identified is not very high. Families are left not knowing what happened to their loved ones. It's traumatic to them for the rest of their lives," says Kate Spradley, an anthropology professor and director of Operation Identification.

"When everybody thinks about the crisis, the number of people trying to cross the border, they don't think about the people who die. There is a huge death toll," Spradley says.

She says "federal policies" are partly to blame for the toll, saying unauthorized migrants are being pushed to make more dangerous overland journeys on foot because of increased border enforcement.

"And it's left to local jurisdictions to deal with," Spradley says. "They're overwhelmed."

The students working on the latest case open a plastic sack that was buried with the body bag. Sometimes it's not the bones that help identify a decedent but the items found with the body, such as a crucifix, a stuffed animal, a baseball or distinctive clothing.

"Oh, definitely personal effects," says one of the students. "Yeah, looks like shoes and a shirt or a jacket."

Spradley says families sometimes have a cellphone picture of the migrant from the day the person left, showing what that person was wearing that day.

"So if we're putting those clothes online, families will recognize those clothes sometimes," she says.

And sometimes, it's the sneakers.

Zaira Gonzalez recognized one familiar pair on NamUs.gov.

"There was a pair of shoes, blue Nikes, that were found with that body that matched a picture of my brother that I have, that had those Nike shoes," she says.

For five years, Gonzalez feared the worst. The last time her family had heard from her brother, Christian, he was with a smuggler trekking through ranch land in Brooks County. He called their father and said he was tired and didn't want to walk any longer. That was on Sept. 9, 2012.

"The end of September, I kept telling my parents something ain't right," Gonzalez says. "We haven't heard anything from him. The human trafficker, we haven't heard anything from him. [Christian] just went missing completely."

The Gonzalez family, from Monterrey, Mexico, had been living in the quiet East Texas town of Palestine. Christian, who was undocumented, got picked up by immigration agents and was deported. After a few unhappy months in Reynosa, Mexico, he crossed the Rio Grande and started for home in Palestine. He'd just turned 23.

His body was found by border agents. He was buried, like other migrants, as John Doe in Sacred Heart Cemetery. His remains eventually made it to Operation Identification. Last year, a DNA test confirmed the remains were Christian's.

"Part of me was telling me that hopefully it's not him," Gonzalez says. "But I was actually relieved because it was him, because now I knew where he was at, taken care of by those students."

The Gonzalez family was able to give him a proper funeral last April. His gravesite is decorated with soccer balls. It was his favorite sport.

But few relatives of missing migrants get this kind of closure.

The South Texas Human Rights Center, a nonprofit that works with migrants and their families, reports that 280 families are actively looking for a loved one who disappeared somewhere on the journey north.

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