SAN MARCOS — A drone flew over the sprawling hills of Freeman Ranch about two years ago, capturing a monochromatic photograph. The gray landscape was grass and dirt and the white spots denoted excessive vegetation. The black flecks were decomposing corpses.

It was exactly the picture that Daniel Wescott, a forensic anthropologist, and Gene Robinson, the owner of a search and rescue organization, were looking for to prove their suspicions that a plane equipped with the right technology could locate the dead.

“We just had one of those eureka moments,” said Robinson, who is based in Wimberley. “We can put these two things together and suddenly we have a forensic tool.”

The ranch is home to about 50 human corpses donated to the Forensic Anthropology Center at Texas State University, which uses them to conduct research that can help medical examiners identify bodies, rescuers find missing persons and law enforcement solve crimes.

Dead bodies are peppered across Texas State’s gated 26 acres on Freeman Ranch. Some are completely decayed down to bones loosely covered by tan, leathery skin, while more recent arrivals resemble the living except for the swollen flesh and colonies of flies laying eggs in facial orifices.

Wescott is the director of the center, known informally as a “body farm." He helps design many of the research projects in the hopes that by controlling the conditions the body decomposes in — and knowing the biological facts of the person who died — the studies can offer insight on murders or unexplained deaths when much less information is available.

The drone flights are part of an ongoing study using near infrared imaging to detect corpses above and below the ground that are often not visible to the naked eye. The technology can also spot locations where a corpse was previously buried for up to two years after it has been removed.

“The search for clandestine bodies is a very time-consuming ordeal,” Wescott said. “Even then, a lot of times you can walk right by them and not realize that they’re there.”

Near infrared imaging picks up reflectance; as a corpse decays it releases carbon and nitrogen into the soil, decreasing the amount of light the soil reflects. At first, the influx of chemicals kills plants, but as it disperses into the area around the body it turns into a fertilizer causing extra vegetation, which reflects a lot of light.

The two extremes show up as black and white on the mostly gray near infrared imaging, giving anyone looking for a body, Robinson said, double the chances of finding of it.

The Texas State labs, which opened in 2008, are constantly churning out research. The placement and conditions of the bodies are purposeful; many are protected by metal-pole cages, but those that aren’t resemble a collection of scattered bones, pillaged by vultures and raccoons. Corpses are above and below ground as well as in both the sun and shade to compare the decay of each. Some bodies are wrapped tightly in tarp, part of a new study that will look at the rate of decay for a common modus operandi of disposal for murders.

The center grabbed national attention recently when it collected the remains of 80 undocumented immigrants who died after crossing the border. Found in a mass grave in Brooks County, the bodies were buried haphazardly, some covered only by trash bags and shopping bags.

Kate Spradley, a researcher and associate professor of anthropology at Texas State, leads a team working to identify the immigrants and send their remains home. The work is slow, and so far the team has confirmed three identities.

But Spradley’s research on ancestry estimation using skeletal measurements could help. After collecting data from Mexicans and Guatemalans, she found they had, on average, slight variations in skull shape — for example, different measurements in the face or in the back of the head. She is working to expand the database to include those from Honduras and El Salvador — where many Texas immigrants originate — which could make identifying remains much more expedient.

“If I’m writing a case report, this person would likely be considered Hispanic, but working on the border, that really is kind of meaningless," Spradley said. "I’m still trying to amass a lot of data from different countries … that really narrows the search.”

Another research project focuses on predatory birds common in arid climates. The center’s 2012 study on vultures greatly helped medical examiners gauge the time of death and better identify an unknown corpse, said Jennifer Love, who met with the center’s researchers when she was the director of forensic anthropology for the Harris County Institute of Forensic Sciences. The research brought forward crucial information: Vultures can render a body into a skeleton in a matter of hours — a time frame previously estimated to be weeks.

“There are a lot of people who have gone missing,” said Love, who now works as a forensic anthropologist in Washington, D.C. "If we’re saying, ‘Okay, an individual has to be dead for at least three weeks’ but in fact has only been dead a day, then we are excluding the person who may actually be the match.”

At the ranch, corpses lay out in the field for a time period of six months to two years. But much of the research takes place post-decomposition on the skeletons, which are carefully stored in boxes that line the walls of the Texas State labs.

These studies typically involve using bones to determine the sex, age and time elapsed since the person died. One graduate student is working on a project that uses only teeth to determine the season of death. Each permanent tooth is anchored to gums twice a year by tiny, distinct fibers; a bright line is laid in the spring or summer and a dark line in the fall or winter. The number of bands, and the color and width of the outermost one, can help estimate the age at death and when a person died.

Texas State researchers meet with law enforcement and forensic professionals to create research plans with clear practical uses. The center also has done corpse tests for defense attorneys and consulted for the FBI, Wescott said.

To share its research, the center hosts workshops for anthropology students, police and medical examiners, who get a tour of the ranch and learn tools to evaluate corpses at crime scenes. When Sgt. Sam Stock from the Hays County Sheriff's Office visited about 18 months ago, he learned to study the insect infestation surrounding a corpse.

“That’s a viable piece of evidence in a potential homicide,” he said. “How far the larvae has developed can give an idea of potentially how long a body has been there. Before, maggots on a body were normal. Nobody really paid attention to it.”

The sheer number of corpses available at the center means its researchers have the resources they need to pull together experiments and the statistical analysis to be confident in the results. Besides the San Marcos ranch, there are a handful of body farms scattered across the United States, including another in Texas at Sam Houston State University in Huntsville, one at Southern Illinois University in Carbondale, Illinois, and another at Western Carolina University in Cullowhee, North Carolina.

The first body farm was founded in the early 1980s at the University of Tennessee at Knoxville by William Bass, a Tennessee state forensic anthropologist. Frustrated by the difficulty of estimating the time of death on a recovered body, Bass began to collect donated corpses for research.

Each center provides research on decomposition with the climate, animals and insects common to its region. Texas State, with its location in an arid climate, makes key discoveries on how extreme heat and vultures can speed up or slow down the decay of a human body.

“We wouldn’t know that if other centers like Texas hadn’t opened,” Dawnie Steadman, director of Tennessee’s Forensic Anthropology Center, said of the Texas State body farm. “We need data and understanding of what’s going in human decomposition in multiple environments.”

See more photos of the body farm here (warning: some pictures are graphic and show decomposing corpses).

Disclosure: The Texas State University System is a corporate sponsor of The Texas Tribune. A complete list of Tribune donors and sponsors can be viewed here.