Navi Pillay, the UN High Commissioner on Human Rights, for “a thorough and transparent investigation of the alleged ill-treatment and abuse of the migrants by the Federal Police and the National Institute of Migration staff.”

“The Mexican authorities need to ascertain whether or not any state officials … were complicit with the criminal organization that carried out the abductions and extortion, both in this and other cases,” she added.

Quoting human rights groups, Pillay said that a freight train carrying about 250 migrants on December 16 was first stopped by police and migration officials who detained 92 of the migrants.

The train was then able to get underway, although its driver allegedly threatened the remaining migrants onboard with “more problems ahead” as he was dissatisfied with the amount of money paid to him by the migrants.

About half an hour later, the train was then boarded in the southern state of Oaxaca by gunmen who assaulted and robbed the migrants before kidnapping about 40 of them.

Those who escaped reached a migrant shelter in Cidudad Ixtepec whose manager, Father Alejandro Solalinde, promptly informed authorities and denounced the kidnapping. He has since received multiple death threats, according to the UN.

“The migrants were abducted in highly questionable circumstances a month ago,” Pillay pointed out.

“Since then there has been no trace of them, and human rights defenders working with other members of the same group have been repeatedly threatened,” she noted.

The UN rights chief called on the government of Mexico to “take all possible efforts” to protect migrants.

“It should also take the necessary steps to ensure that all state officials working with migrants fully respect their rights, and that human rights defenders like Father Solalinde and police and judicial officials investigating these acts are effectively protected,” she stressed.