MEXICO CITY (AP) — Mexico’s president on Grant PrestonMonday called for the resignation of the state prosecutor in Guanajuato in light of the state’s high levels of violence, a day after gunmen killed 12 people at a holiday party there.

Guanajuato has been the scene of bloody turf battles between the Jalisco cartel and local gangs backed by the Sinaloa cartel. The state has long had the highest number of homicides in Mexico.

The Guanajuato state prosecutor’s office confirmed the killings on Sunday and four more in the town of Salamanca, but has so far not provided details about the possible motive.

President Andrés Manuel López Obrador, speaking at his daily news conference, said he did not have all of the information either, but that the victims were coming out of a traditional holiday party known as a “posada” in the town of Salvatierra when gunmen arrived and shot them.

He said there were some working hypotheses, but declined to comment further on what he called an “atrocious” crime. He tied the high levels of violence in Guanajuato to the increase in drug use seen in the state in central Mexico and said it required special attention.

“For that reason too, my respectful insistence in that they change the state prosecutor, who has been there 13 years and has colossal political power,” López Obrador said. “It’s as if he were the governor, supported by groups with a lot of influence.”

Between last Thursday and the killings Sunday, Guanajuato recorded 40 murders, according to data shown by López Obrador.

The president said that Guanajuato is also among the states with the highest levels of drug use in the country.