The bodies of congressman Moises Villanueva and his driver were found in a river in Guerrero, southern Mexico, almost two weeks after they disappeared.
The state prosecutor said that the men had been killed soon after they went missing on September 4, and were still wearing the same clothes when they were found on Saturday.
Both victims had a bullet wound in the head, and were found in a river close to the town of Humuxtitlan. They were last seen leaving a party thrown by a politician in the region.
The authorities have ruled out the theory that the killing was a kidnapping gone wrong, as no demand for ransom money was ever received, according to Proceso.
Investigators have not yet determined the motive for the murders, but Borderland Beat notes that Villanueva had been involved in a campaign to set up a special commission to investigate crimes against migrants.