Several cities in neighboring Sonora were hit by violence Thursday.

Gunfights broke out in San Luis Rio Colorado on the Arizona-Sonora border and Rosario de Tesopaco in the state’s southeast. There were also reports of gunfire in the coastal cities of Empalme and Guaymas, where prisoners also set mattresses on fire during an attempted riot.

Sonora’s Attorney General Claudia Indira Contreras said that one of the four killed in the shootout between suspected criminal groups in San Luis was a former cop that intelligence reports tied to alleged criminal activities, and could have been one of the factors behind the violence.

In Rosario, two people were killed and two vehicles were burned. Another security official says that a new state police base will be established there to help maintain security.