Authorities in Mexico have arrested a man suspected of involvement in the brutal murder of the mayor of the city of Chilpancingo last month.

The murder of Alejandro Arcos, whose decapitated body was found just days after he was sworn in as mayor, has sparked shock and disgust in the violence-torn state of Guerrero.

On Tuesday, police detained Chilpancingo’s top security official, Germán Reyes, for his alleged role in the murder.

Germán Reyes denied involvement in the crime and said he was used as a scapegoat.

Human rights groups have long warned that local security forces in Mexico are infiltrated by powerful criminal gangs who bribe, blackmail and threaten local officials into obeying them.

The brutal murder of Mayor Arcos within a week of his October 1 inauguration and the arrest of Reyes on Tuesday are seen by many in Chilpancingo as further evidence of local criminal groups’ attempts to tighten their grip on the city and authorities.

Reyes, a retired captain who headed the Guerrero state prosecutor’s office for serious crimes before taking over as Chilpancingo’s acting security chief, was named as the prime suspect in the mayor’s murder, sending further shockwaves through the city.

Much of the violence in Chilpancingo stems from a bloody conflict between a criminal gang called Los Ardillos and rival local crime group Los Tlacos.

Los Ardillos specializes in drug trafficking in the state of Guerrero but has reportedly expanded into extortion and other lucrative criminal enterprises.

Its members are also trying to take control of the city’s security forces.

According to Mexican security minister Omar García Harfuch, Mayor Arcos had traveled unaccompanied and without a security detail to an area controlled by Los Ardillos “for a meeting” when he was killed.

Prosecutors have so far provided few details about why they suspect Germán Reyes was involved in the murder.

Reyes told the judge he had “no reason” to harm the mayor and said it was Mayor Arcos who appointed him as the city’s security chief.

Meanwhile, the federal government has deployed more than 12,000 soldiers and National Guard members to the state.

Confronting the wave of violence in Guerrero and other hotspots of cartel and gang violence is one of the main challenges facing President Claudia Sheinbaum, who took office Oct. 1.

During his presidential campaign, Sheinbaum rejected the “militaristic” approach of former Mexican President Felipe Calderon, who declared war on the cartels in 2006, as ineffective.

Instead, he vowed to continue the approach of his predecessor, Andrés Manuel López Obrador, who avoided directly confronting the cartels and argued that doing so would only lead to more bloodshed.

Since being sworn in as president, he has said his government would work to solve crimes and combat widespread impunity by creating a national intelligence system.