Two car bombs exploded in the northeastern Mexican state of Tamaulipas on Friday, where 72 Central and South American migrants were killed at a ranch and an official investigating the massacre went missing.

The cars exploded outside the studios of the national TV network Televisa in the state capital, Ciudad Victoria. There were no casualties, but the blasts added to a sense of fear after the worst single act of violence in the country's drug wars.

The prosecutor, Roberto Jaime Suarez, vanished on Wednesday in the town of San Fernando, where the migrants' bodies were found, the Tamaulipas state attorney general's office said in a statement. A police officer was also missing.

President Felipe Calderón said Suarez, a Tamaulipas state prosecutor, was involved in the initial investigation into the massacre, which authorities have blamed on the Zetas drug gang. The federal attorney general's office is now leading the case.

Meanwhile, investigators continued the process of identifying the victims, with 20 named by midday on Friday. The migrants, 14 of them women, came from at least four countries, including Honduras, El Salvador, Brazil and Ecuador. They were found near a barn after navy personnel stormed the ranch on Tuesday.

The massacre was discovered after an Ecuadorian migrant, who had been left for dead, escaped. Luis Freddy Lala Pomavilla, 18, said the migrants had been kidnapped by armed men who identified themselves as belonging to the Zetas, one of the cartels fighting for supremacy in the state. He said the killing began after they refused offers to work for the cartel.

Interviewed at their home in a remote Andean village by Ecuadorian TV, Lala's family said he had left for the US two months ago after paying $15,000 (£9,000) to a people smuggler to organise the trip.

"I told him not to go, but he went," said one of his seven brothers, Luis Alfredo. His 17-year-old pregnant wife Maria said she had received a call a few weeks ago from Guatemala, indicating all that was well.

Ecuador has complained that Lala's security has been put at risk by the publication of his identity around the world. Mexican newspapers said he had been transferred to a naval base. His family in Ecuador was put under police protection.

The massacre has focused attention on the vulnerability of US-bound economic migrants as they cross Mexico. Since at least 2008 organised crime groups have preyed on migrants, primarily from Central America. Copycat groups might also be using the name of the infamously violent cartel to terrify their victims. A report by Mexico's national commission of human rights in 2009 estimated that more than 1,600 migrants were kidnapped every month.

Typically, the aim has been to force relatives in the US to pay a ransom. Activists have also documented many cases of complicity within the Mexican authorities.

In a chilling testimony published in El Universal newspaper this week, a Salvadoran identified as Marisolina described being forced to cook and clean for the kidnappers as other migrants disappeared if they could not raise the ransom.

"They kept the ones who couldn't pay tied up in a room waiting to be killed," she said. "I would give them food in the morning and next day they wouldn't be there and new ones would be in their place."