MEXICO CITY (AP) — Authorities in northern Mexico said Sunday that a drug gang was behind the shooting attack on a city hall that killed a feminist activist and a bodyguard.

One attacker also died in the Thursday shooting outside the city hall in Guaymas, in the northern border state of Sonora. He was killed when police returned fire.

State prosecutor Claudia Contreras also said at least one hand grenade was used in the attack, but that it appeared to have hit a car.

The intended target may have been the Guaymas police chief, based on threats he had received, Contreras said.

But those that died were one of the chief’s bodyguards and Lucero Marisol, a participant in a rally at city hall marking the International Day for the Elimination of Violence Against Women.

Marches and demonstrations were held around the world on Thursday to mark the day, but it appears the women in Guaymas were hit simply because they were meeting with the city’s mayor and police chief.

“The attack was not directed at the feminist demonstration,” Contreras said.

She said the attacker has since been posthumously identified as a 49-year-old window cleaner.

“The gunman … was recruited by a criminal group because he had addiction problems,” Contreras said.

Two people — an employee of the city press office and another bodyguard — were also wounded in the attack.

The shooting occurred one day after state authorities said they found 14 clandestine graves near Miguel Aleman, a town north of Guaymas.

State prosecutors say the burial pits contained bones, some burned, and decomposing bodies, but said they cannot yet determine the number of victims.

Sonora has been the scene of drug gang turf battles thought to involve factions of the Sinaloa Cartel, allies of the Jalisco cartel and a gang allied with fugitive drug lord Rafael Caro Quintero.