CIUDAD CUAUHTEMOC, Mexico — A pair of rubber-gloved hands carefully separates the red "Evidence" tape from a paper bag and empties the contents onto a table. Hundreds of burnt bone fragments spill out.

The fragments look like bits of volcanic pumice. Yet for the hands that gently smooth them out over the table top, each one bears a name and holds a piece of a story that nobody knows, but that someone, somewhere is desperate to hear.

The fragments laid out by investigators for the Argentine Forensic Anthropology Team are among the remains of tens of thousands of people who have simply disappeared in Mexico's long and bloody drug war. These bones come from one of three isolated ranches in the city of Cuauhtemoc in the northern border state of Chihuahua, where bodies of victims were dissolved or burned in drums.

As President Enrique Pena Nieto prepares to leave office later this year, another administration has come and gone with little progress in solving one of Mexico's biggest problems: the disappeared. Distrust of Mexican authorities runs deep, and many families see the Argentine experts as the only ones to offer any answers to suffering that has stretched on for a decade or more.

In January, Mexico passed a "very important" law that introduces good methods for conducting searches and classifying crimes, said Ariel Dulitzky, director of the Human Rights Clinic at the University of Texas at Austin. But the law still needs funding and political will for enforcement, he said.

Meanwhile, the disappearances continue: 21,286 in this administration so far since Dec. 1, 2012.

Cuauhtemoc, a rural hub, has only 170,000 people, but is nicknamed "the capital of the disappeared" for its relatively high rate of abductions. The state prosecutor's office has listed 676 disappearance cases in the region since 2008, and 395 are missing just within the city.

During a Father's Day celebration held by the Munoz family on June 21, 2011, some strangers came around and threw out insults, according to family members. A fight broke out, and the family called police. One of the Munoz men threw a radio from a patrol car out the window, sparking angry threats, the family said.

A few hours later, a dozen pickup trucks with armed, uniformed men wearing ski masks turned up the house. The men burst into the home and said they were looking for the radio.

"We all ran," said Emma Veleta, the family matriarch, standing next to a banner with the photos of her husband, four sons, a grandson and a nephew who were taken away that day.

One of her sons held onto her and pleaded, "Mom, don't let them take me!" But it was useless. The women were tossed to the floor.

"It was here that they grabbed them out of my hands," Veleta said. "I never saw them again, I just heard their shouts."

They took eight men in all. The authorities have made little progress since in finding out what happened.

Seven years after the Munoz disappearances, the only thing the family has found is a belt buckle that could have belonged to Toribio Munoz, Veleta's 61-year-old husband. A child recognized it among the thousands of charred fragments being analyzed by the Argentines. Local prosecutors wanted to close the case, but the family is still waiting for evidence.

"Nothing has been proven," said Luisa Munoz, Toribio's sister and the mother of Luis Romo, then 21, who disappeared that day.

The family thinks the police were involved in the disappearances and that explains the state government's failure to act. Assistant state prosecutor Jesus Manuel Carrasco said those who were there that day have since left the force.

"We cannot dismiss the possibility that they directly participated, but there is no evidence for it," he said.

The Argentine team always works with official permission so its results will be accepted in court. In Cuauhtemoc, the Argentines came in only after Gov. Cesar Duarte — now accused of several crimes and on the run — left office in December 2016. They have made 13 identifications so far in the area, all from burned bone fragments found on rural ranches at the end of 2011.

The first identification was of Amir Gutierrez, a 33-year-old mechanic who disappeared in 2011. A vertebra turned out to be Amir's bone.

His mother, Idalia Gutierrez, talks about the moment the Argentine investigators told her they had a DNA match. It was difficult news to hear, but also a kind of relief.

"I wanted to find him, alive or dead," she said. "In my mind, I was telling myself, I cannot cry, I have to be calm, because if you cry you don't understand what they are explaining to you."

Mercedes Doretti, the head of the forensic team for Mexico and Central America, said the investigators prepare carefully to deliver such news to families, because it is a "tremendously difficult moment."

The Argentines try to leave nothing unexamined, nothing to chance, so a family is left without doubts — even if there is nothing to bury.

"Sometimes the bone fragments are so small, you can't physically give them anything," she said. "Then there is an issue of trust."

In the last of the boxes from the Dolores Ranch, the gloved hands have chosen 109 fragments that may contain DNA or other useful information to be sent to a laboratory in Argentina.

The rest is carefully swept into an envelope, every last ash, and closed and sealed.

In the meantime, Luisa Munoz does not want to leave her house and her little store in a dusty Cuauhtemoc neighborhood, in case one day Luis calls or returns.

Or in case one day, the Argentines give her a piece of bone that will make her cry.