Police said they found federal lawmaker Moises Villanueva de la Cruz near the highway where he went missing after a party Sept. 4, and were trying to determine what led to his slaying, CNN reported.
"It could be simply a personal matter. We don't know. But whatever it is, we want to know soon," said Rep. Carlos Flores Rico of the Institutional Revolutionary Party.
Villanueva disappeared after attending a party with other politicians in Tlapa, Guerrero, local police and party members said.
Forensic evidence indicated that Villanueva and his driver, found Saturday, had been dead for more than a week, CNN reported. The Interior Ministry pledged federal assistance in the investigation.
Party members said authorities must investigate whether Villanueva's death was tied to his political activities.
"It is very unfortunate ... the climate of instability which is engulfing the country," said Fausto Vallejo Figueroa, a gubernatorial candidate in the central state of Michoacan.
Authorities also reported Monday three teachers were killed in an ambush Monday in Guerrero state. Earlier in September, the state teacher's union said hundreds of schools closed because of threats of violence.