The dead body of a top leader of Mexico's Party of the Democratic Revolution (PRD) for southern Oaxaca state was found on Thursday and police are investigating his death as a homicide, the state attorney general's office said.
Nicolas Estrada, president of the PRD's state council in Oaxaca, one of the leftist party's strongholds, likely died several days before his body was found, officials said.
The attorney general's office said that Estrada, 32, was reported missing since June 15, and his body was found in the town of Tuxtepec, Oaxaca, with three gunshot wounds to the head.
Oaxaca state is currently governed by the PRD, and local elections next month pit the ruling Institutional Revolutionary Party, or PRI, of President Enrique Pena Nieto against a coalition made up of the PRD and the conservative National Action Party, or PAN.
Shortly after taking office in December, Pena Nieto forged the so-called "Pact for Mexico," signed by the government and the country's three major political parties to push through reforms.
Jesus Zambrano, the PRD's national president, offered his condolences to Estrada's family in a post on his Twitter account.
"We demand justice!" he added.
Pena Nieto has vowed to quell the lawlessness and killing that have stained Mexico's image as a tourist destination and rattled investors.
An estimated 70,000 people have been killed in drug-related violence in Mexico over the past seven years.