Mexican authorities have arrested seven suspects in connection with last month's massacre of nine Mormon women and children in the country's north, the attorney general's office said.
A local police chief suspected of links to organized crime was among those taken into custody, according to local media.
The victims -- six of them children -- had dual US-Mexican nationality and were shot dead on a rural road in a lawless region known for turf wars between drug cartels fighting over lucrative trafficking routes to the United States.
Investigators believe the cartel mistook the families for members of a rival gang, but some relatives reject that theory, saying they were deliberately targeted.
The prosecutor's office said in a statement Monday that three suspects were arrested on December 26 for "probable responsibility" in organized crime. The charges against the other four, arrested earlier, were not specified.
The November 4 killing took place between the states of Sonora and Chihuahua and increased pressure on President Andres Manuel Lopez Obrador's government to show it was acting against brutal violence by drug cartels.
Following the massacre, US President Donald Trump threatened to designate drug cartels as terror groups, which many Mexicans saw as opening the door to further meddling by the US.
Lopez Obrador met with relatives of the victims earlier this month to report on the investigation.
A second meeting between the family and Mexican authorities is expected in coming days.