MEXICO CITY – The buses crawled to a halt to obey roadblocks manned by armed men, who boarded like military or police doing an inspection. One by one, they tapped certain passengers, all men, mostly young, to get off: "You. You. You."

Relatives and travel companions watched in horror as the buses pulled away without them. Less than two weeks later, security forces following reports of abducted passengers in violent Tamaulipas state bordering Texas stumbled on a collection of pits holding a total of 59 bodies.

The grisly discovery early Wednesday came in virtually the same spot near the town of San Fernando where 72 migrants were murdered in August and on the same day several thousand people across Mexico took to the streets to say they were fed up with the violence. The United States' top drug enforcer said in Mexico a day earlier that the violence means authorities are winning.

By Thursday, investigators had identified a few victims of the latest massacre as Mexicans, not transnational migrants trying to reach the U.S. They did not say if they were connected to 12 official missing-person reports from the buses. Authorities interviewing witnesses calculated that from 65 to 82 people went missing, Tamaulipas state Interior Secretary Morelos Canseco said.

They were kidnapped on one of Mexico's most dangerous stretches of highway that runs along Mexico's Gulf coast to the border with Texas, an area where federal authorities launched a major offensive in November seeking to regain control of territory from two warring drug gangs, the Gulf Cartel and the Zetas.

Despite an estimated 1,000 soldiers in Tamaulipas, criminals have become so brazen they apparently kidnapped dozens of passengers in a stretch of open desert that locals say lay between two military checkpoints. The Mexican military would not comment on the location of roadblocks for security reasons.

Authorities speculated the men who were pulled off the buses had fallen victim to ever more brutal recruiting efforts to replenish cartel ranks. But one local politician, who didn't want to be identified for safety reasons, said there were rumors that the Gulf Cartel was sending buses of people to fight the Zetas, who control that stretch of road and who began boarding buses in search of their rivals.

The Zetas are blamed for the migrant killings last August as well as the death of U.S. Immigration and Customs Agent Jaime Zapata in neighboring San Luis Potosi state.

There are many more missing in San Fernando, the politician said, adding that "if they keep looking they'll find more and more mass graves."