In the border city of Nuevo Laredo, Tamaulipas, nine bodies were found on a bridge on Friday, reported the AFP. A “narco-banner,” signed in the name of a drug gang, was left next to the bodies, but its contents have not been revealed by authorities. Seven more corpses were dumped on a highway in the municipality of San Fernando, also in Tamaulipas, the same day, reported Milenio. All 16 had been killed by gunshots, and most had their hands tied.

In the neighboring state Nuevo Leon, seven people were executed in a mechanics shop in the city of Monterrey, Blog del Narco reported.

InSight Crime Analysis

Gulf Cartel leader Jorge Eduardo Costilla Sanchez, alias "El Coss," was captured in Tamaulipas two days before the bodies were found. It is possible that the killings were prompted by supporters seeking revenge for the capture -- the drug boss was reportedly arrested after a group of his bodyguards led marines to his house.

There has been bitter infighting within the Gulf Cartel in recent years, and according to some reports El Coss had been carrying out a campaign of betraying his associates to the authorities in order to rid himself of rivals. Gulf boss Mario Cardenas Guillen or "El Gordo" was captured on September 3, and may have handed over information to the authorities about El Coss.

Another possibility is that these mass killings are part of a bid by one of his associates to gain control of the cartel. The death and capture of many of the Gulf Cartel old guard has left the drug trafficking organization without a clear leader to succeed El Coss. Mexican media reports say that a Gulf lieutenant named Mario Armando Ramirez Treviño, alias "X-20" or "Pelon," (pictured, above) may be poised to take control of the organization. He is thought to be the current head of the Reynosa "plaza," or drug trafficking territory, and Vanguardia reported that his ascension to the leadership could mean the end of the divide between rival factions the Rojos and the Metros. 

However, the massacres in northeast Mexico may not be related to El Coss' capture. The Gulf Cartel is disputing the region with the Zetas, which is currently in the throes of a bloody split between its two main leaders. Like the arrest of the Gulf boss, the break between Heriberto Lazcano, alias “El Lazca,” and Miguel Angel Treviño Morales, alias “Z-40,” has shaken up the dynamics  in Mexico's underworld, and is likely to cause more bloodshed in their territory.