Pablo Cote dialed his father's cell phone for 24 hours after he failed to return from a business trip to San Fernando, a town near the U.S. border where the body count from 10 mass graves rose to 72 on Friday.
Finally a strange man answered: "Stop bothering me. He doesn't have this phone anymore. If you keep bothering me, you'll see what happens."
Though he had yet to identify the body, Cote said his father's driver's license was recovered in one of the graves as people across Mexico contacted authorities in search of the disappeared, including dozens who vanished from buses as they crossed the same part of northern Mexico headed to the United States.
Federal authorities said they are holding 14 people _ 12 men and two women _ as suspects in the second mass killing in violent Tamaulipas state, the scene of a massacre of 72 migrants last August.
The federal Attorney General's Office said there was evidence that most of the suspects belonged to the Zetas drug gang, the same group blamed for the August massacre. Some were detained with military-style uniforms, and others were found driving a pickup truck with false Mexican navy insignia.
The suspects are being held under a form of house arrest while under investigation for possible organized crime, weapons and kidnapping charges.
But no one could explain the horror of innocent civilians pulled off buses and out of cars on a well-traveled stretch of highway patrolled by the Mexican military that runs near the Gulf Coast to the U.S. border.
"How sick do you have to be to commit such atrocities," said Cote, whose 55-year-old father traveled from their home in central Tlaxcala state to pick up a minivan in late March. The family buys and sells used cars.
"Killing and mutilating people just because you can," Cote, 32, said amid the stench outside the morgue in Matamoros, a city across the border from Brownsville, Texas, where the bodies were taken.
As investigators looked for more mass graves, calls from people and state governments around Mexico about the missing shed new light on the problem of the drug war's disappeared. More than 34,600 people have died in drug-related violence since President Felipe Calderon launched his offensive against organized crime in late 2006, but no one knows how many people are missing at the hands of drug cartels.
The National Human Rights Commission recently reported it has registered 5,397 people who have gone missing since 2006, but stressed they were not all drug-related. Spokesman Cesar Correa said such a study has never been done.
All day on Friday families were turned away in Matamoros as morgue officials said they would have no information until at least Monday. State authorities are still not sure about the origin of the victims found in the pits.
The majority of victims were men, though four women were among the bodies that authorities started to recover on April 1 while investigating reports that gunmen had begun stopping buses and pulling off some passengers in the area in late March.
Federal security spokesman Alejandro Poire said the suspects led authorities to the pits. The suspects belonged to a "criminal cell," he said, but he did not specify which one.
Authorities speculate the men pulled off the buses fell victim to ever more brutal recruiting efforts by cartels to replenish their ranks. But one local politician, who didn't want to be quoted by name for safety reasons, said there were rumors that the Gulf cartel was sending buses of people to fight its rival, the Zetas, who control that stretch of road and who began boarding buses in search of enemies.
Investigators interviewing witnesses on the bus abductions calculated that from 65 to 82 people went missing, according to Tamaulipas state Tamaulipas state Interior Secretary Morelos Canseco.
Some who came to the morgue had no reason to believe their missing relatives would have been in San Fernando in late March, when the complaints first came in.
Margarita Avellaneda, 41, clutched the flier she has posted around Matamoros since her husband disappeared in October. Gustavo Contreras, 54, was looking for a cousin also not heard from since October as he hitched a ride with the San Fernando mayor-elect. Both vanished.
Ambrosio Leon Rodriguez, 60, came looking for his brother-in-law, who has been missing since he went to board a bus in February in the Tamaulipas port city of Tampico.
"We don't know why they disappeared, but we want to know if they're here," said Avellaneda, whose husband went to pick up a friend near their home in Matamoros. Neither have been heard from since.
Griselda Guerrero, 22, said her relatives disappeared on a bus in Tamaulipas in March 2010 as they headed with other migrants to the U.S. They never found a trace of the bus or the passengers, she said.
Tamaulipas authorities have heard from officials in several states across Mexico looking for residents reported missing from buses that had crossed Tamaulipas, Canseco said.
Susana Montero, a spokeswoman for the Guanajuato state attorney general, said 17 residents of the state haven't been heard from since taking an Omnibus de Mexico bus to northern Mexico in March. The bus route and exact date were unknown, but Montero said they were apparently traveling to the United States.
An official with the Mexican Attorney General's Office said 43 residents of the central states of Queretaro, Hidalgo and San Luis Potosi headed to the U.S. in buses disappeared in March and early April. The official agreed to disclose those details only if she wasn't quoted by name because she was not authorized to talk about the investigation.
"We have information that they got to the state of Tamaulipas," the official said.
Relatives who have filed missing-person reports across Mexico are sending DNA samples to Mexico City, she added.
Michoacan state Attorney General Jesus Mandujano said at least 13 residents of that western state have disappeared in Tamaulipas. In addition, Mandujano said, an unknown number of people from the city of Uruapan went missing while traveling in a bus to Tamaulipas.
One family in Morelia, the Michoacan state capital, said the last text message they received from their 25-year-old son Juan said his bus was arriving in San Fernando. That was in late March, and the family hasn't heard from him since.
The family, who asked not to be identified for fear of reprisals, said they had finally located the bus driver. The driver told them the bus had been stopped by armed men in four sport utility vehicles. The assailants, dressed in black and carrying assault rifles, forced nine men and two women off the bus, and then allowed the vehicle to continue on its way.
Local prosecutors have told the family that one of the bodies found in San Fernando had a tattoo and clothing that matched their description of Juan. The family has provided DNA samples to help positively identify the body.
Canseco told the Milenio television channel that he had yet to hear from other countries, particularly those in Central America, the origin of thousands of migrants who cross Mexico each year on their way to the U.S. He said initial evidence indicated most, if not all, of the victims were Mexicans.
The victims of the massacre last August were from El Salvador, Honduras, Guatemala, Ecuador and Brazil. Survivors said they were killed for refusing to work for the Zetas. Fourteen of those bodies still have not been identified.
Although a federal offensive has been under way in the region since November, criminals have become so brazen they apparently kidnapped the bus passengers on a stretch of highway that area people say lay between two military checkpoints.
Cote said he and his father, also named Pablo Cote, traveled the road often between Tlaxcala and Tamaulipas for their used-car business, passing through military and federal police roadblocks. He said they knew about the dead migrants and heard stories of crimes along the road, but they never saw anything strange.
When they were in San Fernando, sometimes they would see armed men, Cote said.
"There they are," the locals would say.
He said his father arrived in San Fernando by bus on March 30 and stayed only a few hours before heading back to Tlaxcala. He told his son he would call when he reached Tampico. He was never heard from again. He left behind Cote and four daughters.
The family did everything together.
"I don't have words," Cote said. "My family is destroyed ... as the days go by, the pain only increases."
While San Fernando is seldom visited by foreigners, one prime Mexican tourist town _ Taxco, in southern Guerrero state, famous for its silver jewelry _ was also the scene of violence Friday, when gunmen shot it out with local police. Four gunmen and one police officer died, state police reported.
Associated Press writers Adriana Gomez Licon in Mexico City and Gustavo Ruiz in Morelia, Mexico, contributed to this report.