A specialist examines crawling creatures collected from clandestine graves as part of a research project to help locate missing people, in Guadalajara, Mexico, on July 11. (AP photo)

ZAPOPAN, Mexico — First the scientists dress dead swine in clothes, then they dispose of the carcasses. Some they wrap in packing tape, others they chop up. They stuff the animals into plastic bags or wrap them in blankets. They cover them in lime or burn them. Some are buried alone, others in groups.

Then they watch.

The pigs are playing an unlikely role as proxies for humans in research to help find the staggering number of people who have gone missing in Mexico during decades of drug cartel violence.

Families of the missing are usually left to look for their loved ones with little support from authorities. But now, government scientists are testing the newest satellite, geophysical and biological mapping techniques — along with the pigs — to offer clues that they hope could lead to the discovery of at least some of the bodies.

130K missing

The ranks of Mexico’s missing exploded in the years following the launch of then-President Felipe Calderón’s war against drug cartels in 2006. A strategy that targeted the leaders of a handful of powerful cartels led to a splintering of organized crime and the multiplication of violence to control territory.

With near complete impunity, owing to the complicity or inaction of the authorities, cartels found that making anyone they think is in their way disappear was better than leaving bodies in the street. Mexican administrations have sometimes been unwilling to recognize the problem and at other times are staggered by the scale of violence their justice system is unprepared to address.

Mexico’s disappeared could populate a small city. Official data in 2013 tallied 26,000 missing, but the count now surpasses 130,000 — more than any other Latin American nation. The United Nations has said there are indications that the disappearances are “generalized or systematic.”

If the missing people are found — dead or alive — it is usually by their loved ones. Guided by information from witnesses, parents and siblings search for graves by walking through cartel territory, plunging a metal rod into the earth and sniffing for the scent of death.

Plants, insects are keys

Silván walks by a site where scientists buried 14 pigs about two years ago. He says they may not know how well the technology works, where and when it can be used, or under what conditions, for at least three years.

“Flowers came up because of the phosphorous at the surface, we didn’t see that last year,” he said as he took measurements at one of the gravesites. “The mothers who search say that that little yellow flower always blooms over the tombs and they use them as a guide.”

Pigs and humans are closely related, famously sharing about 98% of DNA. But for the mapping project, the physical similarities also matter. According to the U.S. National Library of Medicine, pigs resemble humans in size, fat distribution and the structure and thickness of skin.

A big Colombian drone mounted with a hyperspectral camera flies over the pig burial site. Generally used by mining companies, the camera measures light reflected by substances in the soil, including nitrogen, potassium, phosphorus, and shows how they vary as the pigs decompose. The colorful image it produces offers clues of what to look for in the hunt for graves.

“This isn’t pure science,” Silván said. “It is science and action. Everything learned has to be applied immediately, rather than wait for it to mature, because there’s urgency.”

Researchers also employ thermal drones, laser scanners and other gadgets to register anomalies, underground movements and electrical currents.