Mexico’s new government has been shaken by the murder of a city mayor who was attacked and beheaded days after taking office.

Alejandro Arcos Catalán was sworn in as the mayor of Chilpancingo, the capital of the southern state of Guerrero, on 30 September, a day before Mexico’s first female president, Claudia Sheinbaum, took power herself.

On Monday, less than a week into her presidency, Sheinbaum confirmed reports that the 43-year-old city leader had been slain the previous day, telling reporters: “All the necessary investigations are taking place.”

Photographs of Arcos Catalán’s bloodied head, exhibited on the roof of a white vehicle while his body lay slumped inside, spread on social media – a terrible reminder of the violence that Mexico’s organised crime conflict has inflicted on the Latin American country.

The mayor’s murder came after two close allies were shot dead in the early days of his short-lived administration. A secretary, Francisco Tapia, was gunned down on 3 October, while Ulises Hernández Martínez, a former special forces police commander who was tipped to become Arcos Catalán’s security chief, was riddled with bullets on the eve of the mayor’s inauguration.