The police chief of the Mexican border city of Nuevo Laredo is missing and two of his brothers have been murdered, prosecutors said.
Roberto Alejandro Balmori Garza's whereabouts is not known and orders have been given to find the municipal police chief, the Tamaulipas state Attorney General's Office said in a statement.
Prosecutors, however, did not say what theories investigators had about the police chief's disappearance.
The bodies of Manuel and Jose Alberto Balmori Garza, two of the police chief's brothers, were found Monday in a vehicle parked on the highway that links Monterrey and Nuevo Laredo.
The two men had been shot to death, officials said.
Manuel Balmori Garza was a federal Attorney General's Office agent.
Nuevo Laredo, a city of some 400,000 located across the Rio Grande from Laredo, Texas, is the third most violent city in Mexico after the Pacific resort of Acapulco and the north-central city of Torreon, a recent private report concluded.
Nuevo Laredo police chief Gen. Manuel Farfan Carriola, four bodyguards and an aide were gunned down in February 2011.
Farfan had served as Nuevo Laredo public safety secretary for just 33 days when he was killed.
He was one of nine former military officers hired to take over the command of police departments in Tamaulipas.
The Gulf and Los Zetas drug cartels have been fighting for control of Nuevo Laredo and smuggling routes into the United States.
After several years as the armed wing of the Gulf cartel, Los Zetas, originally a band of Mexican special forces deserters, went into the drug business on their own account and now control several lucrative territories.
The war on drugs launched by former President Felipe Calderon, who was in office from 2006 to 2012, left about 70,000 people dead in Mexico, the government said.
A total of 1,104 people died in violent incidents in Mexico in January, the government said in a report earlier this month.
Of the 1,104 people who died in January in incidents linked to drug cartels and other organized crime groups, 1,068 were suspected criminals and 30 were police officers, soldiers and other public officials "who fell in the line of duty," the report said.
Mexican press tallies estimated that about 12,000 people died in violent incidents linked to organized crime groups in 2012. EFE