The top security official in Chilpancingo was arrested on Tuesday in connection with the murder of the mayor of the Guerrero state capital last month.

Germán Reyes Reyes, a former army captain who became interim head of the Chilpancingo Public Security Ministry on Sept. 30, was detained by state and federal security forces for the murder of Alejandro Arcos Catalán on October 6, the Guerrero Attorney General’s Office (FGE) said in a statement.

A judge in Chilpancingo had issued a warrant for his arrest, the FGE said.

Arcos, 43, was killed just six days after he was sworn in as mayor of Chilpancingo, a city of around 280,000 people. His decapitated body was found inside his pickup truck in the state capital. His head was left on top of the vehicle.

Reyes, a former head of the Guerrero Prosecutor’s Office for Serious Crimes, denied he committed the crime during a court hearing on Tuesday.

“I am a scapegoat,” he said, asserting that he had no motive to commit a crime against the mayor.

Reyes also said he knew “absolutely nothing” about the murder of Arcos and didn’t know why he was arrested. “This is a political matter,” he said.

The Chilpancingo government acknowledged the arrest of the security chief in a statement, and expressed its “firm respect” for the investigations into his alleged involvement in the murder of Arcos.

Just hours before Reyes’ arrest, federal Security Minister Omar García Harfuch said that the mayor was apparently killed by the same gang responsible for the murders in Chilpancingo last week of 11 market vendors, among whom were four boys. Harfuch didn’t name the gang, but a local human rights activist said Los Ardillos was responsible for killing the market vendors, the Associated Press reported.

The arrest of Reyes suggests he may have colluded with Los Ardillos, which is involved in a long-running and extremely violent turf war with the Los Tlacos gang in Chilpancingo. The rival criminal groups are vying for full control over a range of illegal activities including drug trafficking and extortion.

If Reyes is convicted of murdering the former mayor, it would be “a stinging rebuke for a policy adopted by cities across Mexico of hiring retired military officers for top local police jobs, on the assumption that they are less prone to corruption,” AP reported.

Arcos’ murder came just three days after Chilpancingo government secretary, Francisco Gonzalo Tapia, was shot dead in the center of the state capital.

On Sept. 27, the former director of the Special Forces Unit of the Guerrero state police, Ulises Hernández, was killed in Chilpancingo. He was to become security minister in the state capital during the mayorship of Arcos.

With reports from Reforma, Milenio, El Financiero, El País, AP and El Economista