Authorities in the northern Mexican city of Torreon found a severed head and ten decapitated bodies in a pickup truck on the outskirts of the city on Sunday morning.
The other nine heads were discovered later in three different points around the city.
As El Siglo de Torreon reports, city officials said that a note was found accompanying the bodies, though they declined to reveal its contents. Authorities said that eight of the dead were between the ages of 20 and 35, while two were older than 40. Three of those killed were women.
Local army units mobilized in response to the discovery, though no suspects were captured, and officials did not offer any theories to explain the murders.
For the past four years, the Torreon metropolitan area has been the site of increasing violence, driven by clashes between the Zetas and Sinaloa Cartel. The city gained notoriety in 2010 for a series of attacks on bars, linked to the Zetas, in which dozens of people unaffiliated with organized crime were killed.