SAN ANDRES LARRAINZAR, Mexico (AP) — Hundreds of people turned out Tuesday for the burial of Catholic priest Marcelo Pérez, an activist for Indigenous peoples and farm laborers who was killed in the southern Mexico state of Chiapas.

Some 2,000 mourners shouted slogans like “Justice for Marcelo.” The Rev. Pérez had worked tirelessly to bring peace to the highlands and border regions of Chiapas, where two drug cartels are battling for control.

State prosecutors announced they had detained a man suspected of carrying out the killing, but they did not reveal his identity or provide a possible motive in Sunday's killing.

Nonetheless, federal prosecutors announced they are taking over the case, a move that suggests they think organized crime was involved in the killing.

Pérez was laid to rest in his hometown of San Andrés Larrainzar. He was a member of the Tzotzil indigenous group and was among the relatively small number of indigenous priests in Chiapas.

Pérez, 50, had often received threats, but nonetheless continued to work as a peace activist. Human rights advocates said Pérez did not receive the government protection he needed.

“For years, we insisted that the Mexican government should address the threats and aggressions against him, but they never implemented measures to guarantee his life, security and well-being,” The Fray Bartolome de las Casas human rights center wrote.

While there was no immediate information on the killing — President Claudia Sheinbaum only said that “investigations are being carried out” — Rev. Pérez’s peace and mediation efforts may have angered one of the drug cartels.

Chiapas state is a lucrative route for smuggling both drugs and migrants.

“Father Marcelo Pérez was the subject of constant threats and aggressions on the part of organized crime groups,” according to the rights center, adding that his killing “occurred in the context of a serious escalation of violence against the public in all the regions of Chiapas.”

For at least the last two years, the Sinaloa and Jalisco cartels have been engaged in bloody turf battles that involve killing whole families and forcing villagers to take sides in the dispute. Hundreds of Chiapas residents have had to flee to neighboring Guatemala for their own safety.