MEXICO CITY (AP) — A mayoral candidate in a city in northern Mexico was killed Thursday, the latest in a string of attacks that have cost the lives of more than three dozen people running for office.

The killing took place in the northern border state of Sonora. The victim, Albel Murrieta, was also a former state attorney general. The state prosecutors’ office did not say how he died, but a video showed him laying inert on a sidewalk with blood on his face and what appeared to be a spent shell casing lying nearby.

“I condemn those who carried out this cowardly attack,” said the current state Attorney General Claudia Indira.

Murrieta was the candidate of the small Citizen’s Movement party for mayor of the township that covers the city of Ciudad Obregon, Sonora and surrounding areas. The area has been the scene of bloody turf battles between several cartels and allied gangs seeking to control the lucrative smuggling route to the U.S. border.

According to the Etellekt consulting firm, 31 candidates have been killed between September and April in Mexico, making it the second-most violent election since 2000, behind only the 2018 campaign. Most of the candidates killed were vying for nominations or running for local or state posts.

Clemente Castañeda, the Citizen’s Movement national coordinator, called Murrieta “an honorable man, with a spotless career” and said his killing was “an attack on democracy in Sonora.”

He confirmed that Murrieta had also acted as a legal adviser for the LeBaron family, most of whose members are U.S. dual citizens and some of whose relatives were killed in the 2019 ambush slayings of nine U.S.-Mexican dual citizens near the northern border.

The three women and six children from the extended Langford, LeBaron and Miller families were ambushed and slain by suspected drug gang assassins on Nov. 4, 2019.

Initial investigations suggested a squad of gunmen from a drug gang that originated in the border city of Ciudad Juarez set up the ambush to kill members of a rival cartel. However, relatives of the victims say that at some point, the gunmen must have known who they were killing.

Adrian LeBarón wrote in his Twitter account, “They have killed my defender! Today they decided to kill the person who defended us legally. What do we call this? The rule of law?”