The bodies of 58 men and 14 women were discovered on Tuesday when Marines manning a checkpoint on a highway in the northern state of Tamaulipas were approached by a wounded man who said he had been attacked by gang gunmen at a nearby ranch.
A federal official said that man had identified himself an illegal migrant. The man said he and other migrants had been kidnapped by an armed group and taken to the ranch in San Fernando, a town about 100 miles south of Brownsville, Texas, according to the federal official, who had access to the investigation.
He spoke on condition of anonymity because the was not authorized to speak publicly about the case. The official said police believe the migrants were mostly from Central America.
It was unclear if all 72 were killed at the same time — or why.
Another federal official, who also spoke on condition of anonymity, said investigators believe the victims were killed within recent days.
The newspaper Reforma, citing a police report, reported that the migrants had refused to pay extortion fees demanded by the armed group. The federal officials could not immediately confirm that.
Investigators had not determined who was behind the massacre. But one of the federal officials noted that the area is controlled by the Zetas drug cartel, which has diversified into trafficking of migrants trying to reach the United States.
Drug gangs often demand payment from migrants trying to cross the border and sometimes kidnap them, holding them hostage while demanding money from relatives in the United States or their home countries.
More than 28,000 people in Mexico have died in drug violence since Calderon launched his drug fight in late 2006.