Mexican marines has arrested seven gunmen suspected of participating in the massacre of 72 Central and South American migrants, the government has announced.
Four of the suspects were arrested after a September 3 gunbattle with marines, and the other three were captured days later, spokesman, Mr Alejandro Poire, said at a news conference on Wednesday.
Marines alerted by a survivor who managed to escape the mass slaying found the bodies of the migrants on August 24 at a ranch in the northern state of Tamaulipas.
Poire alleged the seven detainees belong to the Zetas drug gang, but he gave no further details on their identities.
Investigators believe the migrants were killed because they refused to work for the Zetas. If true, it would be the worst drug cartel massacre in Mexico to date.
The arrests were announced one day after authorities found the bodies of two men believed to be those of a state detective and a local police chief who participated in the initial investigation of the massacre.
The two police offers went missing a day after the bodies were found in San Fernando, a town about 80 kilometres south of Brownsville, Texas.
The Tamaulipas state Attorney General's Office said Tuesday that identification documents found on the bodies matched those of the missing officials, state detective Roberto Suarez Vazquez and Juan Carlos Suarez Sanchez, who was head of the Public Safety department of San Fernando.